LCOV - code coverage report
Current view: top level - src/reduced_basis - rb_eim_construction.C (source / functions) Hit Total Coverage
Test: libMesh/libmesh: #4229 (6a9aeb) with base 727f46 Lines: 0 1473 0.0 %
Date: 2025-08-19 19:27:09 Functions: 0 85 0.0 %
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          Line data    Source code
       1             : // rbOOmit: An implementation of the Certified Reduced Basis method.
       2             : // Copyright (C) 2009, 2010 David J. Knezevic
       3             : 
       4             : // This file is part of rbOOmit.
       5             : 
       6             : // rbOOmit is free software; you can redistribute it and/or
       7             : // modify it under the terms of the GNU Lesser General Public
       8             : // License as published by the Free Software Foundation; either
       9             : // version 2.1 of the License, or (at your option) any later version.
      10             : 
      11             : // rbOOmit is distributed in the hope that it will be useful,
      12             : // but WITHOUT ANY WARRANTY; without even the implied warranty of
      13             : // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      14             : // Lesser General Public License for more details.
      15             : 
      16             : // You should have received a copy of the GNU Lesser General Public
      17             : // License along with this library; if not, write to the Free Software
      18             : // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
      19             : 
      20             : // C++ includes
      21             : #include <fstream>
      22             : #include <sstream>
      23             : 
      24             : // LibMesh includes
      25             : #include "libmesh/sparse_matrix.h"
      26             : #include "libmesh/numeric_vector.h"
      27             : #include "libmesh/dense_matrix.h"
      28             : #include "libmesh/dense_vector.h"
      29             : #include "libmesh/dof_map.h"
      30             : #include "libmesh/libmesh_logging.h"
      31             : #include "libmesh/equation_systems.h"
      32             : #include "libmesh/parallel.h"
      33             : #include "libmesh/parallel_algebra.h"
      34             : #include "libmesh/fe.h"
      35             : #include "libmesh/quadrature.h"
      36             : #include "libmesh/utility.h"
      37             : #include "libmesh/fe_interface.h"
      38             : #include "libmesh/fe_compute_data.h"
      39             : #include "libmesh/getpot.h"
      40             : #include "libmesh/exodusII_io.h"
      41             : #include "libmesh/fem_context.h"
      42             : #include "libmesh/elem.h"
      43             : #include "libmesh/int_range.h"
      44             : 
      45             : // rbOOmit includes
      46             : #include "libmesh/rb_construction_base.h"
      47             : #include "libmesh/rb_eim_construction.h"
      48             : #include "libmesh/rb_eim_evaluation.h"
      49             : #include "libmesh/rb_parameters.h"
      50             : #include "libmesh/rb_parametrized_function.h"
      51             : 
      52             : // C++ include
      53             : #include <limits>
      54             : #include <memory>
      55             : #include <random>
      56             : 
      57             : namespace libMesh
      58             : {
      59             : 
      60             : namespace
      61             : {
      62             : // We make an anonymous namespace for local helper functions. The helper functions below
      63             : // are used to do some basic operators for QpDataMap and SideQpDataMap.
      64             : 
      65             : // Recall that we have:
      66             : // typedef std::map<dof_id_type, std::vector<std::vector<Number>>> QpDataMap;
      67             : // typedef std::map<std::pair<dof_id_type,unsigned int>, std::vector<std::vector<Number>>> SideQpDataMap;
      68             : 
      69             : // Implement u <- u + k*v
      70             : template <typename DataMap>
      71           0 : void add(DataMap & u, const Number k, const DataMap & v)
      72             : {
      73           0 :   for (auto & [key, vec_vec_u] : u)
      74             :     {
      75           0 :       const std::vector<std::vector<Number>> & vec_vec_v = libmesh_map_find(v, key);
      76             : 
      77           0 :       libmesh_error_msg_if (vec_vec_u.size() != vec_vec_v.size(), "Size mismatch");
      78             : 
      79           0 :       for (auto i : index_range(vec_vec_u))
      80             :         {
      81           0 :           libmesh_error_msg_if (vec_vec_u[i].size() != vec_vec_v[i].size(), "Size mismatch");
      82           0 :           for (auto j : index_range(vec_vec_u[i]))
      83             :             {
      84           0 :               vec_vec_u[i][j] += k*vec_vec_v[i][j];
      85             :             }
      86             :         }
      87             :     }
      88           0 : }
      89             : 
      90           0 : void add_node_data_map(RBEIMConstruction::NodeDataMap & u, const Number k, const RBEIMConstruction::NodeDataMap & v)
      91             : {
      92           0 :   for (auto & [key, vec_u] : u)
      93             :     {
      94           0 :       const std::vector<Number> & vec_v = libmesh_map_find(v, key);
      95             : 
      96           0 :       libmesh_error_msg_if (vec_u.size() != vec_v.size(), "Size mismatch");
      97             : 
      98           0 :       for (auto i : index_range(vec_u))
      99             :         {
     100           0 :           vec_u[i] += k*vec_v[i];
     101             :         }
     102             :     }
     103           0 : }
     104             : 
     105             : }
     106             : 
     107           0 : RBEIMConstruction::RBEIMConstruction (EquationSystems & es,
     108             :                                       const std::string & name_in,
     109           0 :                                       const unsigned int number_in)
     110             :   : RBConstructionBase(es, name_in, number_in),
     111           0 :     best_fit_type_flag(PROJECTION_BEST_FIT),
     112           0 :     _Nmax(0),
     113           0 :     _set_Nmax_from_n_snapshots(false),
     114           0 :     _Nmax_from_n_snapshots_increment(0),
     115           0 :     _rel_training_tolerance(1.e-4),
     116           0 :     _abs_training_tolerance(1.e-12),
     117           0 :     _max_abs_value_in_training_set(0.),
     118           0 :     _max_abs_value_in_training_set_index(0)
     119             : {
     120             :   // The training set should be the same on all processors in the
     121             :   // case of EIM training.
     122           0 :   serial_training_set = true;
     123           0 : }
     124             : 
     125           0 : RBEIMConstruction::~RBEIMConstruction () = default;
     126             : 
     127           0 : void RBEIMConstruction::clear()
     128             : {
     129           0 :   RBConstructionBase::clear();
     130             : 
     131           0 :   _rb_eim_assembly_objects.clear();
     132             : 
     133           0 :   _local_parametrized_functions_for_training.clear();
     134           0 :   _local_quad_point_locations.clear();
     135           0 :   _local_quad_point_JxW.clear();
     136           0 :   _local_quad_point_subdomain_ids.clear();
     137             : 
     138           0 :   _local_side_parametrized_functions_for_training.clear();
     139           0 :   _local_side_quad_point_locations.clear();
     140           0 :   _local_side_quad_point_JxW.clear();
     141           0 :   _local_side_quad_point_subdomain_ids.clear();
     142           0 :   _local_side_quad_point_boundary_ids.clear();
     143           0 :   _local_side_quad_point_side_types.clear();
     144             : 
     145           0 :   _local_node_parametrized_functions_for_training.clear();
     146           0 :   _local_node_locations.clear();
     147           0 :   _local_node_boundary_ids.clear();
     148             : 
     149           0 :   _eim_projection_matrix.resize(0,0);
     150           0 : }
     151             : 
     152           0 : void RBEIMConstruction::set_rb_eim_evaluation(RBEIMEvaluation & rb_eim_eval_in)
     153             : {
     154           0 :   _rb_eim_eval = &rb_eim_eval_in;
     155           0 : }
     156             : 
     157           0 : RBEIMEvaluation & RBEIMConstruction::get_rb_eim_evaluation()
     158             : {
     159           0 :   libmesh_error_msg_if(!_rb_eim_eval, "Error: RBEIMEvaluation object hasn't been initialized yet");
     160           0 :   return *_rb_eim_eval;
     161             : }
     162             : 
     163           0 : const RBEIMEvaluation & RBEIMConstruction::get_rb_eim_evaluation() const
     164             : {
     165           0 :   libmesh_error_msg_if(!_rb_eim_eval, "Error: RBEIMEvaluation object hasn't been initialized yet");
     166           0 :   return *_rb_eim_eval;
     167             : }
     168             : 
     169           0 : void RBEIMConstruction::set_best_fit_type_flag (const std::string & best_fit_type_string)
     170             : {
     171           0 :   if (best_fit_type_string == "projection")
     172             :     {
     173           0 :       best_fit_type_flag = PROJECTION_BEST_FIT;
     174             :     }
     175           0 :   else if (best_fit_type_string == "eim")
     176             :     {
     177           0 :       best_fit_type_flag = EIM_BEST_FIT;
     178             :     }
     179           0 :   else if (best_fit_type_string == "pod")
     180             :     {
     181           0 :       best_fit_type_flag = POD_BEST_FIT;
     182             :     }
     183             :   else
     184           0 :     libmesh_error_msg("Error: invalid best_fit_type in input file");
     185           0 : }
     186             : 
     187           0 : void RBEIMConstruction::print_info()
     188             : {
     189             :   // Print out info that describes the current setup
     190           0 :   libMesh::out << std::endl << "RBEIMConstruction parameters:" << std::endl;
     191           0 :   libMesh::out << "system name: " << this->name() << std::endl;
     192           0 :   libMesh::out << "Nmax: " << get_Nmax() << std::endl;
     193           0 :   if (_set_Nmax_from_n_snapshots)
     194             :   {
     195           0 :     libMesh::out << "Overruling Nmax based on number of snapshots, with increment set to "
     196           0 :       << _Nmax_from_n_snapshots_increment
     197           0 :       << std::endl;
     198             :   }
     199           0 :   libMesh::out << "Greedy relative error tolerance: " << get_rel_training_tolerance() << std::endl;
     200           0 :   libMesh::out << "Greedy absolute error tolerance: " << get_abs_training_tolerance() << std::endl;
     201           0 :   libMesh::out << "Number of parameters: " << get_n_params() << std::endl;
     202           0 :   for (const auto & pr : get_parameters())
     203           0 :     if (!is_discrete_parameter(pr.first))
     204             :       {
     205           0 :         libMesh::out <<   "Parameter " << pr.first
     206           0 :                      << ": Min = " << get_parameter_min(pr.first)
     207           0 :                      << ", Max = " << get_parameter_max(pr.first) << std::endl;
     208             :       }
     209             : 
     210           0 :   print_discrete_parameter_values();
     211           0 :   libMesh::out << "n_training_samples: " << get_n_training_samples() << std::endl;
     212           0 :   libMesh::out << "quiet mode? " << is_quiet() << std::endl;
     213             : 
     214           0 :   if (best_fit_type_flag == PROJECTION_BEST_FIT)
     215             :     {
     216           0 :       libMesh::out << "EIM best fit type: projection" << std::endl;
     217             :     }
     218             :   else
     219           0 :     if (best_fit_type_flag == EIM_BEST_FIT)
     220             :       {
     221           0 :         libMesh::out << "EIM best fit type: eim" << std::endl;
     222             :       }
     223           0 :   libMesh::out << std::endl;
     224           0 : }
     225             : 
     226           0 : void RBEIMConstruction::initialize_eim_construction()
     227             : {
     228           0 :   initialize_parametrized_functions_in_training_set();
     229           0 : }
     230             : 
     231           0 : void RBEIMConstruction::process_parameters_file (const std::string & parameters_filename)
     232             : {
     233             :   // First read in data from input_filename
     234           0 :   GetPot infile(parameters_filename);
     235             : 
     236           0 :   std::string best_fit_type_string = infile("best_fit_type","projection");
     237           0 :   set_best_fit_type_flag(best_fit_type_string);
     238             : 
     239           0 :   const unsigned int n_training_samples = infile("n_training_samples",0);
     240           0 :   const bool deterministic_training = infile("deterministic_training",false);
     241           0 :   unsigned int training_parameters_random_seed_in =
     242             :     static_cast<unsigned int>(-1);
     243           0 :   training_parameters_random_seed_in = infile("training_parameters_random_seed",
     244             :                                               training_parameters_random_seed_in);
     245           0 :   const bool quiet_mode_in = infile("quiet_mode", quiet_mode);
     246           0 :   const unsigned int Nmax_in = infile("Nmax", _Nmax);
     247           0 :   const Real rel_training_tolerance_in = infile("rel_training_tolerance",
     248           0 :                                                 _rel_training_tolerance);
     249           0 :   const Real abs_training_tolerance_in = infile("abs_training_tolerance",
     250           0 :                                                 _abs_training_tolerance);
     251             : 
     252             :   // Read in the parameters from the input file too
     253           0 :   unsigned int n_continuous_parameters = infile.vector_variable_size("parameter_names");
     254           0 :   RBParameters mu_min_in;
     255           0 :   RBParameters mu_max_in;
     256           0 :   for (unsigned int i=0; i<n_continuous_parameters; i++)
     257             :     {
     258             :       // Read in the parameter names
     259           0 :       std::string param_name = infile("parameter_names", "NONE", i);
     260             : 
     261             :       {
     262           0 :         Real min_val = infile(param_name, 0., 0);
     263           0 :         mu_min_in.set_value(param_name, min_val);
     264             :       }
     265             : 
     266             :       {
     267           0 :         Real max_val = infile(param_name, 0., 1);
     268           0 :         mu_max_in.set_value(param_name, max_val);
     269             :       }
     270             :     }
     271             : 
     272           0 :   std::map<std::string, std::vector<Real>> discrete_parameter_values_in;
     273             : 
     274           0 :   unsigned int n_discrete_parameters = infile.vector_variable_size("discrete_parameter_names");
     275           0 :   for (unsigned int i=0; i<n_discrete_parameters; i++)
     276             :     {
     277           0 :       std::string param_name = infile("discrete_parameter_names", "NONE", i);
     278             : 
     279           0 :       unsigned int n_vals_for_param = infile.vector_variable_size(param_name);
     280           0 :       std::vector<Real> vals_for_param(n_vals_for_param);
     281           0 :       for (auto j : make_range(vals_for_param.size()))
     282           0 :         vals_for_param[j] = infile(param_name, 0., j);
     283             : 
     284           0 :       discrete_parameter_values_in[param_name] = vals_for_param;
     285             :     }
     286             : 
     287           0 :   std::map<std::string,bool> log_scaling_in;
     288             :   // For now, just set all entries to false.
     289             :   // TODO: Implement a decent way to specify log-scaling true/false
     290             :   // in the input text file
     291           0 :   for (const auto & pr : mu_min_in)
     292           0 :     log_scaling_in[pr.first] = false;
     293             : 
     294             :   // Set the parameters that have been read in
     295           0 :   set_rb_construction_parameters(n_training_samples,
     296             :                                  deterministic_training,
     297             :                                  training_parameters_random_seed_in,
     298             :                                  quiet_mode_in,
     299             :                                  Nmax_in,
     300             :                                  rel_training_tolerance_in,
     301             :                                  abs_training_tolerance_in,
     302             :                                  mu_min_in,
     303             :                                  mu_max_in,
     304             :                                  discrete_parameter_values_in,
     305             :                                  log_scaling_in);
     306           0 : }
     307             : 
     308           0 : void RBEIMConstruction::set_rb_construction_parameters(unsigned int n_training_samples_in,
     309             :                                                        bool deterministic_training_in,
     310             :                                                        int training_parameters_random_seed_in,
     311             :                                                        bool quiet_mode_in,
     312             :                                                        unsigned int Nmax_in,
     313             :                                                        Real rel_training_tolerance_in,
     314             :                                                        Real abs_training_tolerance_in,
     315             :                                                        const RBParameters & mu_min_in,
     316             :                                                        const RBParameters & mu_max_in,
     317             :                                                        const std::map<std::string, std::vector<Real>> & discrete_parameter_values_in,
     318             :                                                        const std::map<std::string,bool> & log_scaling_in,
     319             :                                                        std::map<std::string, std::vector<RBParameter>> * training_sample_list)
     320             : {
     321             :   // Read in training_parameters_random_seed value.  This is used to
     322             :   // seed the RNG when picking the training parameters.  By default the
     323             :   // value is -1, which means use std::time to seed the RNG.
     324           0 :   set_training_random_seed(training_parameters_random_seed_in);
     325             : 
     326             :   // Set quiet mode
     327           0 :   set_quiet_mode(quiet_mode_in);
     328             : 
     329             :   // Initialize RB parameters
     330           0 :   set_Nmax(Nmax_in);
     331             : 
     332           0 :   set_rel_training_tolerance(rel_training_tolerance_in);
     333           0 :   set_abs_training_tolerance(abs_training_tolerance_in);
     334             : 
     335           0 :   if (get_rb_eim_evaluation().get_parametrized_function().is_lookup_table)
     336             :     {
     337             :       const std::string & lookup_table_param_name =
     338           0 :         get_rb_eim_evaluation().get_parametrized_function().lookup_table_param_name;
     339             : 
     340           0 :       libmesh_error_msg_if(!discrete_parameter_values_in.count(lookup_table_param_name),
     341             :         "Lookup table parameter should be discrete");
     342             : 
     343             :       // Make an editable copy of discrete_parameters_values_in.
     344             :       std::map<std::string, std::vector<Real>> discrete_parameter_values_final(
     345           0 :           discrete_parameter_values_in);
     346             : 
     347             :       std::vector<Real> & lookup_table_param_values =
     348           0 :         libmesh_map_find(discrete_parameter_values_final, lookup_table_param_name);
     349             : 
     350             :       // Overwrite the discrete values for lookup_table_param to make sure that
     351             :       // it is: 0, 1, 2, ..., size-1.
     352           0 :       std::iota(lookup_table_param_values.begin(), lookup_table_param_values.end(), 0);
     353             : 
     354             :       // Also, overwrite n_training_samples_in to make sure it matches
     355             :       // lookup_table_size so that we will get full coverage of the
     356             :       // lookup table in our training set.
     357           0 :       n_training_samples_in = lookup_table_param_values.size();
     358             : 
     359             :       // Initialize the parameter ranges and the parameters themselves
     360           0 :       initialize_parameters(mu_min_in, mu_max_in, discrete_parameter_values_final);
     361             :     }
     362             :   else
     363             :     {
     364             :       // Initialize the parameter ranges and the parameters themselves
     365           0 :       initialize_parameters(mu_min_in, mu_max_in, discrete_parameter_values_in);
     366             :     }
     367             : 
     368           0 :   bool updated_deterministic_training = deterministic_training_in;
     369           0 :   if (training_sample_list && (this->get_parameters_min().n_parameters() > 3))
     370             :     {
     371             :       // In this case we force deterministic_training to be false because
     372             :       // a) deterministic training samples are not currrently supported with
     373             :       //    more than 3 parameters, and
     374             :       // b) we will overwrite the training samples anyway in the call to
     375             :       //    load_training_set() below, so we do not want to generate an
     376             :       //    error due to deterministic training sample generation when
     377             :       //    the samples will be overwritten anyway.
     378           0 :       updated_deterministic_training = false;
     379             :     }
     380             : 
     381           0 :   initialize_training_parameters(this->get_parameters_min(),
     382             :                                  this->get_parameters_max(),
     383             :                                  n_training_samples_in,
     384             :                                  log_scaling_in,
     385           0 :                                  updated_deterministic_training);
     386             : 
     387           0 :   if (training_sample_list)
     388             :     {
     389             :       // Note that we must call initialize_training_parameters() before
     390             :       // load_training_set() in order to initialize the parameter vectors.
     391           0 :       load_training_set(*training_sample_list);
     392             :     }
     393             : 
     394             : 
     395           0 :   if (get_rb_eim_evaluation().get_parametrized_function().is_lookup_table)
     396             :     {
     397             :       // Also, now that we've initialized the training set, overwrite the training
     398             :       // samples to ensure that we have full coverage of the lookup tbale.
     399             :       const std::string & lookup_table_param_name =
     400           0 :         get_rb_eim_evaluation().get_parametrized_function().lookup_table_param_name;
     401             : 
     402             :       // Fill the lookup_table_training_samples with sequential single-entry vectors,
     403             :       // i.e. {{0.0}, {1.0}, {2.0}, ...}
     404           0 :       Real val = 0.0;
     405           0 :       std::vector<RBParameter> lookup_table_training_samples(n_training_samples_in, {val});
     406           0 :       for (auto & vec : lookup_table_training_samples)
     407             :         {
     408           0 :           vec[0] = val;
     409           0 :           val += 1.0;   // Could use val++, but better to be explicit for doubles.
     410             :         }
     411             : 
     412           0 :       set_training_parameter_values(lookup_table_param_name, lookup_table_training_samples);
     413           0 :     }
     414           0 : }
     415             : 
     416           0 : Real RBEIMConstruction::train_eim_approximation()
     417             : {
     418           0 :   if (_normalize_solution_snapshots)
     419           0 :     apply_normalization_to_solution_snapshots();
     420             : 
     421           0 :   if(best_fit_type_flag == POD_BEST_FIT)
     422             :     {
     423           0 :       train_eim_approximation_with_POD();
     424           0 :       return 0.;
     425             :     }
     426             :   else
     427             :     {
     428           0 :       return train_eim_approximation_with_greedy();
     429             :     }
     430             : }
     431             : 
     432           0 : Real RBEIMConstruction::train_eim_approximation_with_greedy()
     433             : {
     434           0 :   LOG_SCOPE("train_eim_approximation_with_greedy()", "RBEIMConstruction");
     435             : 
     436           0 :   RBEIMEvaluation & rbe = get_rb_eim_evaluation();
     437             : 
     438             :   // We need space for one extra interpolation point if we're using the
     439             :   // EIM error indicator.
     440           0 :   unsigned int max_matrix_size = rbe.use_eim_error_indicator() ? get_Nmax()+1 : get_Nmax();
     441           0 :   _eim_projection_matrix.resize(max_matrix_size,max_matrix_size);
     442             : 
     443           0 :   rbe.initialize_parameters(*this);
     444           0 :   rbe.resize_data_structures(max_matrix_size);
     445             : 
     446             :   // If we are continuing from a previous training run,
     447             :   // we might already be at the max number of basis functions.
     448             :   // If so, we can just return.
     449           0 :   libmesh_error_msg_if(rbe.get_n_basis_functions() > 0,
     450             :                        "Error: We currently only support EIM training starting from an empty basis");
     451             : 
     452           0 :   libMesh::out << std::endl << "---- Performing Greedy EIM basis enrichment ----" << std::endl;
     453             : 
     454           0 :   if (_max_abs_value_in_training_set <= get_abs_training_tolerance())
     455             :   {
     456           0 :     std::cout << "Maximum absolute value in the training set is "
     457           0 :       << _max_abs_value_in_training_set << ", which is less than or equal to the abs. training tolerance of "
     458           0 :       << get_abs_training_tolerance() << ", hence exiting Greedy basis enrichment with empty basis" << std::endl;
     459           0 :     return 0.0;
     460             :   }
     461             : 
     462             :   // Initialize greedy_error so that we do not incorrectly set is_zero_bf=true on
     463             :   // the first iteration.
     464           0 :   Real greedy_error = -1.;
     465           0 :   std::vector<RBParameters> greedy_param_list;
     466             : 
     467             :   // Initialize the current training index to the index that corresponds
     468             :   // to the largest (in terms of infinity norm) function in the training set.
     469             :   // We do this to ensure that the first EIM basis function is not zero.
     470           0 :   unsigned int current_training_index = _max_abs_value_in_training_set_index;
     471           0 :   set_params_from_training_set(current_training_index);
     472             : 
     473             :   // We use this boolean to indicate if we will run one more iteration
     474             :   // before exiting the loop below. We use this when computing the EIM
     475             :   // error indicator, which requires one extra EIM iteration.
     476           0 :   bool exit_on_next_iteration = false;
     477             : 
     478             :   // We also initialize a boolean to keep track of whether we have
     479             :   // reached "n_samples" EIM basis functions, since we need to
     480             :   // handle the EIM error indicator in a special way in this case.
     481           0 :   bool bfs_equals_n_samples = false;
     482             : 
     483             :   while (true)
     484             :     {
     485           0 :       if (rbe.get_n_basis_functions() >= get_n_training_samples())
     486             :         {
     487           0 :           libMesh::out << "Number of basis functions (" << rbe.get_n_basis_functions()
     488           0 :             << ") equals number of training samples." << std::endl;
     489             : 
     490           0 :           bfs_equals_n_samples = true;
     491             : 
     492             :           // If exit_on_next_iteration==true then we don't exit yet, since
     493             :           // we still need to add data for the error indicator before exiting.
     494           0 :           if (!exit_on_next_iteration)
     495           0 :             break;
     496             :         }
     497             : 
     498           0 :       libMesh::out << "Greedily selected parameter vector:" << std::endl;
     499           0 :       print_parameters();
     500           0 :       greedy_param_list.emplace_back(get_parameters());
     501             : 
     502           0 :       libMesh::out << "Enriching the EIM approximation" << std::endl;
     503             :       libmesh_try
     504             :         {
     505           0 :           bool is_zero_bf = bfs_equals_n_samples || (greedy_error == 0.);
     506             : 
     507             :           // If is_zero_bf==true then we add an "extra point" because we
     508             :           // cannot add a usual EIM interpolation point in that case since
     509             :           // the full EIM space is already covered. This is necessary when we
     510             :           // want to add an extra point for error indicator purposes in the
     511             :           // is_zero_bf==true case, for example.
     512           0 :           std::unique_ptr<EimPointData> eim_point_data;
     513           0 :           if (is_zero_bf)
     514           0 :               eim_point_data = std::make_unique<EimPointData>(get_random_point_from_training_sample());
     515             : 
     516             :           // If exit_on_next_iteration==true then we do not add a basis function in
     517             :           // that case since in that case we only need to add data for the EIM error
     518             :           // indicator.
     519           0 :           enrich_eim_approximation(current_training_index,
     520           0 :                                    /*add_basis_function*/ !exit_on_next_iteration,
     521             :                                    eim_point_data.get());
     522           0 :           update_eim_matrices(/*set_error_indicator*/ exit_on_next_iteration);
     523             : 
     524           0 :           libMesh::out << std::endl << "---- Basis dimension: "
     525           0 :                       << rbe.get_n_basis_functions() << " ----" << std::endl;
     526             : 
     527           0 :           if (get_rb_eim_evaluation().get_parametrized_function().is_lookup_table &&
     528           0 :               best_fit_type_flag == EIM_BEST_FIT)
     529             :             {
     530             :               // If this is a lookup table and we're using "EIM best fit" then we
     531             :               // need to update the eim_solutions after each EIM enrichment so that
     532             :               // we can call rb_eim_eval.rb_eim_solve() from within compute_max_eim_error().
     533           0 :               store_eim_solutions_for_training_set();
     534             :             }
     535             : 
     536           0 :           libMesh::out << "Computing EIM error on training set" << std::endl;
     537           0 :           std::tie(greedy_error, current_training_index) = compute_max_eim_error();
     538           0 :           set_params_from_training_set(current_training_index);
     539             : 
     540           0 :           libMesh::out << "Maximum EIM error is " << greedy_error << std::endl << std::endl;
     541           0 :         }
     542             : #ifdef LIBMESH_ENABLE_EXCEPTIONS
     543           0 :       catch (const std::exception & e)
     544             :         {
     545             :           // If we hit an exception when performing the enrichment for the error indicator, then
     546             :           // we just continue and skip the error indicator. Otherwise we rethrow the exception.
     547           0 :           if (exit_on_next_iteration)
     548             :             {
     549           0 :               std::cout << "Exception occurred when enriching basis for error indicator hence we skip the error indicator in this case" << std::endl;
     550           0 :               break;
     551             :             }
     552             :           else
     553           0 :             throw;
     554           0 :         }
     555             : #endif
     556             : 
     557           0 :       if (exit_on_next_iteration)
     558             :         {
     559           0 :           libMesh::out << "Extra EIM iteration for error indicator is complete, hence exiting EIM training now" << std::endl;
     560           0 :           break;
     561             :         }
     562             : 
     563             :       // Convergence and/or termination tests
     564             :       {
     565           0 :         bool exit_condition_satisfied = false;
     566             : 
     567           0 :         if (rbe.get_n_basis_functions() >= this->get_Nmax())
     568             :           {
     569           0 :             libMesh::out << "Maximum number of basis functions reached: Nmax = "
     570           0 :                           << get_Nmax() << std::endl;
     571           0 :             exit_condition_satisfied = true;
     572             :           }
     573             : 
     574             :         // We consider the relative tolerance as relative to the maximum value in the training
     575             :         // set, since we assume that this maximum value provides a relevant scaling.
     576           0 :         if (!exit_condition_satisfied)
     577           0 :           if (greedy_error < (get_rel_training_tolerance() * get_max_abs_value_in_training_set()))
     578             :             {
     579           0 :               libMesh::out << "Relative error tolerance reached." << std::endl;
     580           0 :               exit_condition_satisfied = true;
     581             :             }
     582             : 
     583           0 :         if (!exit_condition_satisfied)
     584           0 :           if (greedy_error < get_abs_training_tolerance())
     585             :             {
     586           0 :               libMesh::out << "Absolute error tolerance reached." << std::endl;
     587           0 :               exit_condition_satisfied = true;
     588             :             }
     589             : 
     590           0 :         bool has_parameters = (get_parameters().n_parameters() > 0);
     591           0 :         if (!exit_condition_satisfied)
     592             :         {
     593           0 :           bool do_exit = false;
     594             :           // In the check for repeated parameters we have to make sure this isn't a case
     595             :           // with no parameters, since in that case we would always report repeated
     596             :           // parameters.
     597           0 :           for (auto & param : greedy_param_list)
     598           0 :             if (param == get_parameters() && has_parameters)
     599             :               {
     600           0 :                 libMesh::out << "Exiting greedy because the same parameters were selected twice"
     601           0 :                              << std::endl;
     602           0 :                 do_exit = true;
     603           0 :                 break;
     604             :               }
     605             : 
     606           0 :           if (do_exit)
     607           0 :             exit_condition_satisfied = true;
     608             :         }
     609             : 
     610           0 :         if (exit_condition_satisfied)
     611             :           {
     612             :             // If we're using the EIM error indicator then we need to run
     613             :             // one extra EIM iteration since we use the extra EIM point
     614             :             // to obtain our error indicator. If we're not using the EIM
     615             :             // error indicator, then we just exit now.
     616           0 :             if (get_rb_eim_evaluation().use_eim_error_indicator() && has_parameters)
     617             :               {
     618           0 :                 exit_on_next_iteration = true;
     619           0 :                 libMesh::out << "EIM error indicator is active, hence we will run one extra EIM iteration before exiting"
     620           0 :                              << std::endl;
     621             :               }
     622             :             else
     623           0 :               break;
     624             :           }
     625             :       }
     626           0 :     } // end while(true)
     627             : 
     628           0 :   if (rbe.get_parametrized_function().is_lookup_table &&
     629           0 :       best_fit_type_flag != EIM_BEST_FIT)
     630             :     {
     631             :       // We only enter here if best_fit_type_flag != EIM_BEST_FIT because we
     632             :       // already called this above in the EIM_BEST_FIT case.
     633           0 :       store_eim_solutions_for_training_set();
     634             :     }
     635             : 
     636           0 :   return greedy_error;
     637           0 : }
     638             : 
     639           0 : void RBEIMConstruction::apply_normalization_to_solution_snapshots()
     640             : {
     641           0 :   LOG_SCOPE("apply_normalization_to_solution_snapshots()", "RBEIMConstruction");
     642             : 
     643           0 :   libMesh::out << "Normalizing solution snapshots" << std::endl;
     644             : 
     645           0 :   bool apply_comp_scaling = !get_rb_eim_evaluation().scale_components_in_enrichment().empty();
     646           0 :   unsigned int n_snapshots = get_n_training_samples();
     647           0 :   RBEIMEvaluation & rbe = get_rb_eim_evaluation();
     648             : 
     649           0 :   for (unsigned int i=0; i<n_snapshots; i++)
     650             :     {
     651           0 :       Real norm_val = 0.;
     652           0 :       if (rbe.get_parametrized_function().on_mesh_sides())
     653             :         {
     654           0 :           norm_val = std::sqrt(std::real(side_inner_product(
     655           0 :             _local_side_parametrized_functions_for_training[i],
     656           0 :             _local_side_parametrized_functions_for_training[i],
     657             :             apply_comp_scaling)));
     658             : 
     659           0 :           if (norm_val > 0.)
     660           0 :             scale_parametrized_function(_local_side_parametrized_functions_for_training[i], 1./norm_val);
     661             :         }
     662           0 :       else if (rbe.get_parametrized_function().on_mesh_nodes())
     663             :         {
     664           0 :           norm_val = std::sqrt(std::real(node_inner_product(
     665           0 :             _local_node_parametrized_functions_for_training[i],
     666           0 :             _local_node_parametrized_functions_for_training[i],
     667             :             apply_comp_scaling)));
     668             : 
     669           0 :           if (norm_val > 0.)
     670           0 :             scale_node_parametrized_function(_local_node_parametrized_functions_for_training[i], 1./norm_val);
     671             :         }
     672             :       else
     673             :         {
     674           0 :           norm_val = std::sqrt(std::real(inner_product(
     675           0 :             _local_parametrized_functions_for_training[i],
     676           0 :             _local_parametrized_functions_for_training[i],
     677             :             apply_comp_scaling)));
     678             : 
     679           0 :           if (norm_val > 0.)
     680           0 :             scale_parametrized_function(_local_parametrized_functions_for_training[i], 1./norm_val);
     681             :         }
     682             : 
     683             :       // Since we're rescaling the training samples, we should also rescale
     684             :       // _max_abs_value_in_training_set in the same way. We obtained the
     685             :       // _max_abs_value_in_training_set value from the sample with index
     686             :       // _max_abs_value_in_training_set_index, so we rescale using the norm
     687             :       // of this sample here. Note that the value we obtain may not be exactly
     688             :       // equal to the max value we would obtain after looping over all the
     689             :       // normalized samples, because we normalized in the L2 norm rather than
     690             :       // in the max norm, but it should be close to this "true max" value. The
     691             :       // main use-case of _max_abs_value_in_training_set is to scale the relative
     692             :       // error tolerance in the Greedy training, and the L2-norm-scaled value of
     693             :       // _max_abs_value_in_training_set that we obtain here should be sufficient
     694             :       // for that purpose.
     695           0 :       if ((i == _max_abs_value_in_training_set_index) && (norm_val > 0.))
     696           0 :         _max_abs_value_in_training_set /= norm_val;
     697             :     }
     698             : 
     699           0 :   libMesh::out << "Maximum absolute value in the training set after normalization: "
     700           0 :     << _max_abs_value_in_training_set << std::endl << std::endl;
     701           0 : }
     702             : 
     703           0 : Real RBEIMConstruction::train_eim_approximation_with_POD()
     704             : {
     705           0 :   LOG_SCOPE("train_eim_approximation_with_POD()", "RBEIMConstruction");
     706             : 
     707           0 :   RBEIMEvaluation & rbe = get_rb_eim_evaluation();
     708             : 
     709           0 :   unsigned int n_snapshots = get_n_training_samples();
     710             : 
     711             :   // If _set_Nmax_from_n_snapshots=true, then we overrule Nmax.
     712           0 :   if (_set_Nmax_from_n_snapshots)
     713             :   {
     714           0 :     int updated_Nmax = (static_cast<int>(n_snapshots) + _Nmax_from_n_snapshots_increment);
     715             : 
     716             :     // We only overrule _Nmax if updated_Nmax is positive, since if Nmax=0 then we'll skip
     717             :     // training here entirely, which is typically not what we want.
     718           0 :     if (updated_Nmax > 0)
     719           0 :       _Nmax = static_cast<unsigned int>(updated_Nmax);
     720             :   }
     721             : 
     722             :   // _eim_projection_matrix is not used in the POD case, but we resize it here in any case
     723             :   // to be consistent with what we do in train_eim_approximation_with_greedy().
     724             :   // We need space for one extra interpolation point if we're using the
     725             :   // EIM error indicator.
     726           0 :   unsigned int max_matrix_size = rbe.use_eim_error_indicator() ? get_Nmax()+1 : get_Nmax();
     727           0 :   _eim_projection_matrix.resize(max_matrix_size,max_matrix_size);
     728             : 
     729           0 :   rbe.initialize_parameters(*this);
     730           0 :   rbe.resize_data_structures(get_Nmax());
     731             : 
     732           0 :   libmesh_error_msg_if(rbe.get_n_basis_functions() > 0,
     733             :                        "Error: We currently only support EIM training starting from an empty basis");
     734             : 
     735           0 :   libMesh::out << std::endl << "---- Performing POD EIM basis enrichment ----" << std::endl;
     736             : 
     737             :   // Set up the POD "correlation matrix". This enables us to compute the POD via the
     738             :   // "method of snapshots", in which we compute a low rank representation of the
     739             :   // n_snapshots x n_snapshots matrix.
     740           0 :   DenseMatrix<Number> correlation_matrix(n_snapshots,n_snapshots);
     741             : 
     742           0 :   std::cout << "Start computing correlation matrix" << std::endl;
     743             : 
     744           0 :   bool apply_comp_scaling = !get_rb_eim_evaluation().scale_components_in_enrichment().empty();
     745           0 :   for (unsigned int i=0; i<n_snapshots; i++)
     746             :     {
     747           0 :       for (unsigned int j=0; j<=i; j++)
     748             :         {
     749           0 :           Number inner_prod = 0.;
     750           0 :           if (rbe.get_parametrized_function().on_mesh_sides())
     751             :             {
     752           0 :               inner_prod = side_inner_product(
     753           0 :                 _local_side_parametrized_functions_for_training[i],
     754           0 :                 _local_side_parametrized_functions_for_training[j],
     755             :                 apply_comp_scaling);
     756             :             }
     757           0 :           else if (rbe.get_parametrized_function().on_mesh_nodes())
     758             :             {
     759           0 :               inner_prod = node_inner_product(
     760           0 :                 _local_node_parametrized_functions_for_training[i],
     761           0 :                 _local_node_parametrized_functions_for_training[j],
     762             :                 apply_comp_scaling);
     763             :             }
     764             :           else
     765             :             {
     766           0 :               inner_prod = inner_product(
     767           0 :                 _local_parametrized_functions_for_training[i],
     768           0 :                 _local_parametrized_functions_for_training[j],
     769             :                 apply_comp_scaling);
     770             :             }
     771             : 
     772             : 
     773           0 :           correlation_matrix(i,j) = inner_prod;
     774           0 :           if(i != j)
     775             :             {
     776           0 :               correlation_matrix(j,i) = libmesh_conj(inner_prod);
     777             :             }
     778             :         }
     779             : 
     780             :       // Print out every 10th row so that we can see the progress
     781           0 :       if ( (i+1) % 10 == 0)
     782           0 :         std::cout << "Finished row " << (i+1) << " of " << n_snapshots << std::endl;
     783             :     }
     784           0 :   std::cout << "Finished computing correlation matrix" << std::endl;
     785             : 
     786             :   // Compute SVD of correlation matrix.
     787             :   // Let Y = U S V^T, then the SVD below corresponds
     788             :   // to Y^T Y = V S U^T U S V^T = V S^2 V^T.
     789             :   // The POD basis we use is then given by U, which
     790             :   // we can compute via U = Y V S^{-1}, which is what
     791             :   // we compute below.
     792             :   //
     793             :   // Note that the formulation remains the same in the
     794             :   // case that we use a weighted inner product (as
     795             :   // in the case that we used apply_comp_scaling=true
     796             :   // when computing the correlation matrix), see (1.28)
     797             :   // from the lecture notes from Volkwein on POD for more
     798             :   // details.
     799           0 :   DenseVector<Real> sigma( n_snapshots );
     800           0 :   DenseMatrix<Number> U( n_snapshots, n_snapshots );
     801           0 :   DenseMatrix<Number> VT( n_snapshots, n_snapshots );
     802           0 :   correlation_matrix.svd(sigma, U, VT );
     803             : 
     804             :   // We use this boolean to indicate if we will run one more iteration
     805             :   // before exiting the loop below. We use this when computing the EIM
     806             :   // error indicator, which requires one extra EIM iteration.
     807           0 :   bool exit_on_next_iteration = false;
     808             : 
     809             :   // Add dominant vectors from the POD as basis functions.
     810           0 :   unsigned int j = 0;
     811           0 :   Real rel_err = 0.;
     812             : 
     813             :   // We also initialize a boolean to keep track of whether we have
     814             :   // reached "n_snapshots" EIM basis functions, since we need to
     815             :   // handle the EIM error indicator in a special way in this case.
     816           0 :   bool j_equals_n_snapshots = false;
     817             :   while (true)
     818             :     {
     819           0 :       bool exit_condition_satisfied = false;
     820             : 
     821           0 :       if ((j == 0) && (sigma(0) == 0.))
     822             :       {
     823           0 :         libMesh::out << "Terminating EIM POD with empty basis because first singular value is zero" << std::endl;
     824           0 :         exit_condition_satisfied = true;
     825           0 :         rel_err = 0.;
     826             :       }
     827           0 :       else if (j >= n_snapshots)
     828             :         {
     829           0 :           libMesh::out << "Number of basis functions equals number of training samples." << std::endl;
     830           0 :           exit_condition_satisfied = true;
     831           0 :           j_equals_n_snapshots = true;
     832             : 
     833             :           // In this case we set the rel. error to be zero since we've filled up the
     834             :           // entire space. We cannot use the formula below for rel_err since
     835             :           // sigma(n_snapshots) is not defined.
     836           0 :           rel_err = 0.;
     837             :         }
     838             :       else
     839             :         {
     840             :           // The "energy" error in the POD approximation is determined by the first omitted
     841             :           // singular value, i.e. sigma(j). We normalize by sigma(0), which gives the total
     842             :           // "energy", in order to obtain a relative error.
     843           0 :           rel_err = std::sqrt(sigma(j)) / std::sqrt(sigma(0));
     844             :         }
     845             : 
     846           0 :       if (exit_on_next_iteration)
     847             :         {
     848           0 :           libMesh::out << "Extra EIM iteration for error indicator is complete, POD error norm for extra iteration: " << rel_err << std::endl;
     849           0 :           break;
     850             :         }
     851             : 
     852           0 :       libMesh::out << "Number of basis functions: " << j
     853           0 :                    << ", POD error norm: " << rel_err << std::endl;
     854             : 
     855           0 :       if (!exit_condition_satisfied)
     856           0 :         if (j >= get_Nmax())
     857             :           {
     858           0 :             libMesh::out << "Maximum number of basis functions (" << j << ") reached." << std::endl;
     859           0 :             exit_condition_satisfied = true;
     860             :           }
     861             : 
     862           0 :       if (!exit_condition_satisfied)
     863           0 :         if (rel_err < get_rel_training_tolerance())
     864             :           {
     865           0 :             libMesh::out << "Training tolerance reached." << std::endl;
     866           0 :             exit_condition_satisfied = true;
     867             :           }
     868             : 
     869           0 :       if (exit_condition_satisfied)
     870             :         {
     871             :           // If we're using the EIM error indicator then we need to run
     872             :           // one extra EIM iteration since we use the extra EIM point
     873             :           // to obtain our error indicator. If we're not using the EIM
     874             :           // error indicator, then we just exit now.
     875           0 :           bool has_parameters = (get_parameters().n_parameters() > 0);
     876           0 :           if (get_rb_eim_evaluation().use_eim_error_indicator() && has_parameters)
     877             :             {
     878           0 :               exit_on_next_iteration = true;
     879           0 :               libMesh::out << "EIM error indicator is active, hence we will run one extra EIM iteration before exiting"
     880           0 :                             << std::endl;
     881             :             }
     882             :           else
     883           0 :             break;
     884             :         }
     885             : 
     886           0 :       bool is_zero_bf = j_equals_n_snapshots || (rel_err == 0.);
     887           0 :       if (rbe.get_parametrized_function().on_mesh_sides())
     888             :         {
     889             :           // Make a "zero clone" by copying to get the same data layout, and then scaling by zero
     890           0 :           SideQpDataMap v = _local_side_parametrized_functions_for_training[0];
     891             : 
     892           0 :           if (!is_zero_bf)
     893             :             {
     894           0 :               scale_parametrized_function(v, 0.);
     895             : 
     896           0 :               for ( unsigned int i=0; i<n_snapshots; ++i )
     897           0 :                 add(v, U.el(i, j), _local_side_parametrized_functions_for_training[i] );
     898             : 
     899           0 :               Real norm_v = std::sqrt(sigma(j));
     900           0 :               scale_parametrized_function(v, 1./norm_v);
     901             :             }
     902             : 
     903             :           libmesh_try
     904             :             {
     905             :               // If is_zero_bf==true then we add an "extra point" because we cannot
     906             :               // add a usual EIM interpolation point in that case since the full EIM
     907             :               // space is already covered. This is necessary when we want to add an
     908             :               // extra point for error indicator purposes in the is_zero_bf==true
     909             :               // case, for example.
     910           0 :               std::unique_ptr<EimPointData> eim_point_data;
     911           0 :               if (is_zero_bf)
     912           0 :                   eim_point_data = std::make_unique<EimPointData>(get_random_point(v));
     913             : 
     914             :               // If exit_on_next_iteration==true then we do not add a basis function in
     915             :               // that case since in that case we only need to add data for the EIM error
     916             :               // indicator.
     917           0 :               bool is_linearly_dependent = enrich_eim_approximation_on_sides(v,
     918           0 :                                                                              /*add_basis_function*/ !exit_on_next_iteration,
     919             :                                                                              eim_point_data.get());
     920             : 
     921           0 :               if (is_linearly_dependent && !is_zero_bf)
     922             :                 {
     923             :                   // In this case we detected that v is actually linearly dependent and that is_zero_bf
     924             :                   // was previously not correct --- it should have been true. We typically
     925             :                   // catch this earlier (e.g. by checking rel_err) but in some cases we do not catch
     926             :                   // this until we call the enrichment method. In this situation we update is_zero_bf
     927             :                   // to true and call the enrichment again.
     928           0 :                   is_zero_bf = true;
     929           0 :                   eim_point_data = std::make_unique<EimPointData>(get_random_point(v));
     930             : 
     931           0 :                   enrich_eim_approximation_on_sides(v,
     932           0 :                                                     /*add_basis_function*/ !exit_on_next_iteration,
     933             :                                                     eim_point_data.get());
     934             :                 }
     935             : 
     936           0 :               update_eim_matrices(/*set_error_indicator*/ exit_on_next_iteration);
     937           0 :             }
     938             : #ifdef LIBMESH_ENABLE_EXCEPTIONS
     939           0 :           catch (const std::exception & e)
     940             :             {
     941             :               // If we hit an exception when performing the enrichment for the error indicator, then
     942             :               // we just continue and skip the error indicator. Otherwise we rethrow the exception.
     943           0 :               if (exit_on_next_iteration)
     944             :                 {
     945           0 :                   std::cout << "Exception occurred when enriching basis for error indicator hence we skip the error indicator in this case" << std::endl;
     946           0 :                   break;
     947             :                 }
     948             :               else
     949           0 :                 throw;
     950           0 :             }
     951             : #endif
     952             :         }
     953           0 :       else if (rbe.get_parametrized_function().on_mesh_nodes())
     954             :         {
     955             :           // Make a "zero clone" by copying to get the same data layout, and then scaling by zero
     956           0 :           NodeDataMap v = _local_node_parametrized_functions_for_training[0];
     957             : 
     958           0 :           if (!is_zero_bf)
     959             :             {
     960           0 :               scale_node_parametrized_function(v, 0.);
     961             : 
     962           0 :               for ( unsigned int i=0; i<n_snapshots; ++i )
     963           0 :                 add_node_data_map(v, U.el(i, j), _local_node_parametrized_functions_for_training[i] );
     964             : 
     965           0 :               Real norm_v = std::sqrt(sigma(j));
     966           0 :               scale_node_parametrized_function(v, 1./norm_v);
     967             :             }
     968             : 
     969             :           libmesh_try
     970             :             {
     971             :               // If is_zero_bf==true then we add an "extra point" because we cannot
     972             :               // add a usual EIM interpolation point in that case since the full EIM
     973             :               // space is already covered. This is necessary when we want to add an
     974             :               // extra point for error indicator purposes in the is_zero_bf==true
     975             :               // case, for example.
     976           0 :               std::unique_ptr<EimPointData> eim_point_data;
     977           0 :               if (is_zero_bf)
     978           0 :                   eim_point_data = std::make_unique<EimPointData>(get_random_point(v));
     979             : 
     980             :               // If exit_on_next_iteration==true then we do not add a basis function in
     981             :               // that case since in that case we only need to add data for the EIM error
     982             :               // indicator.
     983           0 :               bool is_linearly_dependent = enrich_eim_approximation_on_nodes(v,
     984           0 :                                                                              /*add_basis_function*/ !exit_on_next_iteration,
     985             :                                                                              eim_point_data.get());
     986             : 
     987           0 :               if (is_linearly_dependent && !is_zero_bf)
     988             :                 {
     989             :                   // In this case we detected that v is actually linearly dependent and that is_zero_bf
     990             :                   // was previously not correct --- it should have been true. We typically
     991             :                   // catch this earlier (e.g. by checking rel_err) but in some cases we do not catch
     992             :                   // this until we call the enrichment method. In this situation we update is_zero_bf
     993             :                   // to true and call the enrichment again.
     994           0 :                   is_zero_bf = true;
     995           0 :                   eim_point_data = std::make_unique<EimPointData>(get_random_point(v));
     996             : 
     997           0 :                   enrich_eim_approximation_on_nodes(v,
     998           0 :                                                     /*add_basis_function*/ !exit_on_next_iteration,
     999             :                                                     eim_point_data.get());
    1000             :                 }
    1001             : 
    1002           0 :               update_eim_matrices(/*set_error_indicator*/ exit_on_next_iteration);
    1003           0 :             }
    1004             : #ifdef LIBMESH_ENABLE_EXCEPTIONS
    1005           0 :           catch (const std::exception & e)
    1006             :             {
    1007             :               // If we hit an exception when performing the enrichment for the error indicator, then
    1008             :               // we just continue and skip the error indicator. Otherwise we rethrow the exception.
    1009           0 :               if (exit_on_next_iteration)
    1010             :                 {
    1011           0 :                   std::cout << "Exception occurred when enriching basis for error indicator hence we skip the error indicator in this case" << std::endl;
    1012           0 :                   break;
    1013             :                 }
    1014             :               else
    1015           0 :                 throw;
    1016           0 :             }
    1017             : #endif
    1018             :         }
    1019             :       else
    1020             :         {
    1021             :           // Make a "zero clone" by copying to get the same data layout, and then scaling by zero
    1022           0 :           QpDataMap v = _local_parametrized_functions_for_training[0];
    1023             : 
    1024           0 :           if (!is_zero_bf)
    1025             :             {
    1026           0 :               scale_parametrized_function(v, 0.);
    1027             : 
    1028           0 :               for ( unsigned int i=0; i<n_snapshots; ++i )
    1029           0 :                 add(v, U.el(i, j), _local_parametrized_functions_for_training[i] );
    1030             : 
    1031           0 :               Real norm_v = std::sqrt(sigma(j));
    1032           0 :               scale_parametrized_function(v, 1./norm_v);
    1033             :             }
    1034             : 
    1035             :           libmesh_try
    1036             :             {
    1037             :               // If is_zero_bf==true then we add an "extra point" because we cannot
    1038             :               // add a usual EIM interpolation point in that case since the full EIM
    1039             :               // space is already covered. This is necessary when we want to add an
    1040             :               // extra point for error indicator purposes in the is_zero_bf==true
    1041             :               // case, for example.
    1042           0 :               std::unique_ptr<EimPointData> eim_point_data;
    1043           0 :               if (is_zero_bf)
    1044           0 :                   eim_point_data = std::make_unique<EimPointData>(get_random_point(v));
    1045             : 
    1046             :               // If exit_on_next_iteration==true then we do not add a basis function in
    1047             :               // that case since in that case we only need to add data for the EIM error
    1048             :               // indicator.
    1049           0 :               bool is_linearly_dependent = enrich_eim_approximation_on_interiors(v,
    1050           0 :                                                                                  /*add_basis_function*/ !exit_on_next_iteration,
    1051             :                                                                                  eim_point_data.get());
    1052             : 
    1053           0 :               if (is_linearly_dependent && !is_zero_bf)
    1054             :                 {
    1055             :                   // In this case we detected that v is actually linearly dependent and that is_zero_bf
    1056             :                   // was previously not correct --- it should have been true. We typically
    1057             :                   // catch this earlier (e.g. by checking rel_err) but in some cases we do not catch
    1058             :                   // this until we call the enrichment method. In this situation we update is_zero_bf
    1059             :                   // to true and call the enrichment again.
    1060           0 :                   is_zero_bf = true;
    1061           0 :                   eim_point_data = std::make_unique<EimPointData>(get_random_point(v));
    1062             : 
    1063           0 :                   enrich_eim_approximation_on_interiors(v,
    1064           0 :                                                         /*add_basis_function*/ !exit_on_next_iteration,
    1065             :                                                         eim_point_data.get());
    1066             :                 }
    1067             : 
    1068           0 :               update_eim_matrices(/*set_error_indicator*/ exit_on_next_iteration);
    1069           0 :             }
    1070             : #ifdef LIBMESH_ENABLE_EXCEPTIONS
    1071           0 :           catch (const std::exception & e)
    1072             :             {
    1073             :               // If we hit an exception when performing the enrichment for the error indicator, then
    1074             :               // we just continue and skip the error indicator. Otherwise we rethrow the exception.
    1075           0 :               if (exit_on_next_iteration)
    1076             :                 {
    1077           0 :                   std::cout << "Exception occurred when enriching basis for error indicator hence we skip the error indicator in this case" << std::endl;
    1078           0 :                   break;
    1079             :                 }
    1080             :               else
    1081           0 :                 throw;
    1082           0 :             }
    1083             : #endif
    1084             :         }
    1085             : 
    1086           0 :       if (is_zero_bf)
    1087             :         {
    1088             :           // In this case we exit here instead of increment j and continuing because
    1089             :           // if we've encountered a zero EIM basis function then we must not have
    1090             :           // any more valid data to add.
    1091           0 :           std::cout << "Zero basis function encountered, hence exiting." << std::endl;
    1092           0 :           break;
    1093             :         }
    1094             : 
    1095           0 :       j++;
    1096           0 :     }
    1097           0 :   libMesh::out << std::endl;
    1098             : 
    1099           0 :   return rel_err;
    1100           0 : }
    1101             : 
    1102           0 : void RBEIMConstruction::initialize_eim_assembly_objects()
    1103             : {
    1104           0 :   _rb_eim_assembly_objects.clear();
    1105           0 :   for (auto i : make_range(get_rb_eim_evaluation().get_n_basis_functions()))
    1106           0 :     _rb_eim_assembly_objects.push_back(build_eim_assembly(i));
    1107           0 : }
    1108             : 
    1109           0 : std::vector<std::unique_ptr<ElemAssembly>> & RBEIMConstruction::get_eim_assembly_objects()
    1110             : {
    1111           0 :   return _rb_eim_assembly_objects;
    1112             : }
    1113             : 
    1114           0 : void RBEIMConstruction::init_context(FEMContext & c)
    1115             : {
    1116             :   // Pre-request FE data for all element dimensions present in the
    1117             :   // mesh.  Note: we currently pre-request FE data for all variables
    1118             :   // in the current system but in some cases that may be overkill, for
    1119             :   // example if only variable 0 is used.
    1120           0 :   const System & sys = c.get_system();
    1121           0 :   const MeshBase & mesh = sys.get_mesh();
    1122             : 
    1123           0 :   for (unsigned int dim=1; dim<=3; ++dim)
    1124           0 :     if (mesh.elem_dimensions().count(dim))
    1125           0 :       for (auto var : make_range(sys.n_vars()))
    1126             :       {
    1127           0 :         auto fe = c.get_element_fe(var, dim);
    1128           0 :         fe->get_JxW();
    1129           0 :         fe->get_xyz();
    1130           0 :         fe->get_phi();
    1131             : 
    1132           0 :         auto side_fe = c.get_side_fe(var, dim);
    1133           0 :         side_fe->get_JxW();
    1134           0 :         side_fe->get_xyz();
    1135           0 :         side_fe->get_phi();
    1136             :       }
    1137           0 : }
    1138             : 
    1139           0 : void RBEIMConstruction::set_rel_training_tolerance(Real new_training_tolerance)
    1140             : {
    1141           0 :   _rel_training_tolerance = new_training_tolerance;
    1142           0 : }
    1143             : 
    1144           0 : Real RBEIMConstruction::get_rel_training_tolerance()
    1145             : {
    1146           0 :   return _rel_training_tolerance;
    1147             : }
    1148             : 
    1149           0 : void RBEIMConstruction::set_abs_training_tolerance(Real new_training_tolerance)
    1150             : {
    1151           0 :   _abs_training_tolerance = new_training_tolerance;
    1152           0 : }
    1153             : 
    1154           0 : Real RBEIMConstruction::get_abs_training_tolerance()
    1155             : {
    1156           0 :   return _abs_training_tolerance;
    1157             : }
    1158             : 
    1159           0 : unsigned int RBEIMConstruction::get_Nmax() const
    1160             : {
    1161           0 :   return _Nmax;
    1162             : }
    1163             : 
    1164           0 : void RBEIMConstruction::set_Nmax(unsigned int Nmax)
    1165             : {
    1166           0 :   _Nmax = Nmax;
    1167           0 : }
    1168             : 
    1169           0 : void RBEIMConstruction::enable_set_Nmax_from_n_snapshots(int increment)
    1170             : {
    1171           0 :   _set_Nmax_from_n_snapshots = true;
    1172           0 :   _Nmax_from_n_snapshots_increment = increment;
    1173           0 : }
    1174             : 
    1175           0 : void RBEIMConstruction::disable_set_Nmax_from_n_snapshots()
    1176             : {
    1177           0 :   _set_Nmax_from_n_snapshots = false;
    1178           0 :   _Nmax_from_n_snapshots_increment = 0;
    1179           0 : }
    1180             : 
    1181           0 : Real RBEIMConstruction::get_max_abs_value_in_training_set() const
    1182             : {
    1183           0 :   return _max_abs_value_in_training_set;
    1184             : }
    1185             : 
    1186           0 : void RBEIMConstruction::store_eim_solutions_for_training_set()
    1187             : {
    1188           0 :   LOG_SCOPE("store_eim_solutions_for_training_set()", "RBEIMConstruction");
    1189             : 
    1190           0 :   RBEIMEvaluation & eim_eval = get_rb_eim_evaluation();
    1191             : 
    1192           0 :   std::vector<DenseVector<Number>> & eim_solutions = get_rb_eim_evaluation().get_eim_solutions_for_training_set();
    1193           0 :   eim_solutions.clear();
    1194           0 :   eim_solutions.resize(get_n_training_samples());
    1195             : 
    1196           0 :   unsigned int RB_size = get_rb_eim_evaluation().get_n_basis_functions();
    1197             : 
    1198           0 :   for (auto i : make_range(get_n_training_samples()))
    1199             :     {
    1200           0 :       if (eim_eval.get_parametrized_function().on_mesh_sides())
    1201             :         {
    1202           0 :           const auto & local_side_pf = _local_side_parametrized_functions_for_training[i];
    1203             : 
    1204           0 :           if (RB_size > 0)
    1205             :             {
    1206             :               // Get the right-hand side vector for the EIM approximation
    1207             :               // by sampling the parametrized function (stored in solution)
    1208             :               // at the interpolation points.
    1209           0 :               DenseVector<Number> EIM_rhs(RB_size);
    1210           0 :               for (unsigned int j=0; j<RB_size; j++)
    1211             :                 {
    1212           0 :                   EIM_rhs(j) =
    1213           0 :                     RBEIMEvaluation::get_parametrized_function_side_value(comm(),
    1214             :                                                                           local_side_pf,
    1215             :                                                                           eim_eval.get_interpolation_points_elem_id(j),
    1216             :                                                                           eim_eval.get_interpolation_points_side_index(j),
    1217             :                                                                           eim_eval.get_interpolation_points_comp(j),
    1218             :                                                                           eim_eval.get_interpolation_points_qp(j));
    1219             :                 }
    1220           0 :               eim_solutions[i] = eim_eval.rb_eim_solve(EIM_rhs);
    1221             :             }
    1222             :         }
    1223           0 :       else if (eim_eval.get_parametrized_function().on_mesh_nodes())
    1224             :         {
    1225           0 :           const auto & local_node_pf = _local_node_parametrized_functions_for_training[i];
    1226             : 
    1227           0 :           if (RB_size > 0)
    1228             :             {
    1229             :               // Get the right-hand side vector for the EIM approximation
    1230             :               // by sampling the parametrized function (stored in solution)
    1231             :               // at the interpolation points.
    1232           0 :               DenseVector<Number> EIM_rhs(RB_size);
    1233           0 :               for (unsigned int j=0; j<RB_size; j++)
    1234             :                 {
    1235           0 :                   EIM_rhs(j) =
    1236           0 :                     RBEIMEvaluation::get_parametrized_function_node_value(comm(),
    1237             :                                                                           local_node_pf,
    1238             :                                                                           eim_eval.get_interpolation_points_node_id(j),
    1239             :                                                                           eim_eval.get_interpolation_points_comp(j));
    1240             :                 }
    1241           0 :               eim_solutions[i] = eim_eval.rb_eim_solve(EIM_rhs);
    1242             :             }
    1243             :         }
    1244             :       else
    1245             :         {
    1246           0 :           const auto & local_pf = _local_parametrized_functions_for_training[i];
    1247             : 
    1248           0 :           if (RB_size > 0)
    1249             :             {
    1250             :               // Get the right-hand side vector for the EIM approximation
    1251             :               // by sampling the parametrized function (stored in solution)
    1252             :               // at the interpolation points.
    1253           0 :               DenseVector<Number> EIM_rhs(RB_size);
    1254           0 :               for (unsigned int j=0; j<RB_size; j++)
    1255             :                 {
    1256           0 :                   EIM_rhs(j) =
    1257           0 :                     RBEIMEvaluation::get_parametrized_function_value(comm(),
    1258             :                                                                     local_pf,
    1259             :                                                                     eim_eval.get_interpolation_points_elem_id(j),
    1260             :                                                                     eim_eval.get_interpolation_points_comp(j),
    1261             :                                                                     eim_eval.get_interpolation_points_qp(j));
    1262             :                 }
    1263           0 :               eim_solutions[i] = eim_eval.rb_eim_solve(EIM_rhs);
    1264             :             }
    1265             :         }
    1266             :     }
    1267           0 : }
    1268             : 
    1269           0 : const RBEIMEvaluation::QpDataMap & RBEIMConstruction::get_parametrized_function_from_training_set(unsigned int training_index) const
    1270             : {
    1271           0 :   libmesh_error_msg_if(training_index >= _local_parametrized_functions_for_training.size(),
    1272             :                        "Invalid index: " << training_index);
    1273           0 :   return _local_parametrized_functions_for_training[training_index];
    1274             : }
    1275             : 
    1276           0 : const RBEIMEvaluation::SideQpDataMap & RBEIMConstruction::get_side_parametrized_function_from_training_set(unsigned int training_index) const
    1277             : {
    1278           0 :   libmesh_error_msg_if(training_index >= _local_side_parametrized_functions_for_training.size(),
    1279             :                        "Invalid index: " << training_index);
    1280           0 :   return _local_side_parametrized_functions_for_training[training_index];
    1281             : }
    1282             : 
    1283           0 : const RBEIMEvaluation::NodeDataMap & RBEIMConstruction::get_node_parametrized_function_from_training_set(unsigned int training_index) const
    1284             : {
    1285           0 :   libmesh_error_msg_if(training_index >= _local_node_parametrized_functions_for_training.size(),
    1286             :                        "Invalid index: " << training_index);
    1287           0 :   return _local_node_parametrized_functions_for_training[training_index];
    1288             : }
    1289             : 
    1290           0 : const std::unordered_map<dof_id_type, std::vector<Real> > & RBEIMConstruction::get_local_quad_point_JxW()
    1291             : {
    1292           0 :   return _local_quad_point_JxW;
    1293             : }
    1294             : 
    1295           0 : const std::map<std::pair<dof_id_type,unsigned int>, std::vector<Real> > & RBEIMConstruction::get_local_side_quad_point_JxW()
    1296             : {
    1297           0 :   return _local_side_quad_point_JxW;
    1298             : }
    1299             : 
    1300           0 : unsigned int RBEIMConstruction::get_n_parametrized_functions_for_training() const
    1301             : {
    1302           0 :   if (get_rb_eim_evaluation().get_parametrized_function().on_mesh_sides())
    1303           0 :     return _local_side_parametrized_functions_for_training.size();
    1304           0 :   else if (get_rb_eim_evaluation().get_parametrized_function().on_mesh_nodes())
    1305           0 :     return _local_node_parametrized_functions_for_training.size();
    1306             :   else
    1307           0 :     return _local_parametrized_functions_for_training.size();
    1308             : }
    1309             : 
    1310           0 : void RBEIMConstruction::reinit_eim_projection_matrix()
    1311             : {
    1312           0 :   RBEIMEvaluation & rbe = get_rb_eim_evaluation();
    1313             : 
    1314             :   // We need space for one extra interpolation point if we're using the
    1315             :   // EIM error indicator.
    1316           0 :   unsigned int max_matrix_size = rbe.use_eim_error_indicator() ? get_Nmax()+1 : get_Nmax();
    1317           0 :   _eim_projection_matrix.resize(max_matrix_size,max_matrix_size);
    1318           0 : }
    1319             : 
    1320           0 : std::pair<Real,unsigned int> RBEIMConstruction::compute_max_eim_error()
    1321             : {
    1322           0 :   LOG_SCOPE("compute_max_eim_error()", "RBEIMConstruction");
    1323             : 
    1324           0 :   if (get_n_params() == 0)
    1325             :     {
    1326             :       // Just return 0 if we have no parameters.
    1327           0 :       return std::make_pair(0.,0);
    1328             :     }
    1329             : 
    1330             :   // keep track of the maximum error
    1331           0 :   unsigned int max_err_index = 0;
    1332           0 :   Real max_err = 0.;
    1333             : 
    1334           0 :   libmesh_error_msg_if(get_n_training_samples() != get_local_n_training_samples(),
    1335             :                        "Error: Training samples should be the same on all procs");
    1336             : 
    1337           0 :   const unsigned int RB_size = get_rb_eim_evaluation().get_n_basis_functions();
    1338             : 
    1339           0 :   if(best_fit_type_flag == PROJECTION_BEST_FIT)
    1340             :     {
    1341           0 :       for (auto training_index : make_range(get_n_training_samples()))
    1342             :         {
    1343           0 :           if (get_rb_eim_evaluation().get_parametrized_function().on_mesh_sides())
    1344             :             {
    1345             :               // Make a copy of the pre-computed solution for the specified training sample
    1346             :               // since we will modify it below to compute the best fit error.
    1347           0 :               SideQpDataMap solution_copy = _local_side_parametrized_functions_for_training[training_index];
    1348             : 
    1349             :               // Perform an L2 projection in order to find the best approximation to
    1350             :               // the parametrized function from the current EIM space.
    1351           0 :               DenseVector<Number> best_fit_rhs(RB_size);
    1352           0 :               for (unsigned int i=0; i<RB_size; i++)
    1353             :                 {
    1354           0 :                   best_fit_rhs(i) = side_inner_product(solution_copy,
    1355           0 :                                                        get_rb_eim_evaluation().get_side_basis_function(i),
    1356             :                                                        /*apply_comp_scaling*/ false);
    1357             :                 }
    1358             : 
    1359             :               // Now compute the best fit by an LU solve
    1360           0 :               DenseMatrix<Number> RB_inner_product_matrix_N(RB_size);
    1361           0 :               _eim_projection_matrix.get_principal_submatrix(RB_size, RB_inner_product_matrix_N);
    1362             : 
    1363           0 :               DenseVector<Number> best_fit_coeffs;
    1364           0 :               RB_inner_product_matrix_N.lu_solve(best_fit_rhs, best_fit_coeffs);
    1365             : 
    1366           0 :               get_rb_eim_evaluation().side_decrement_vector(solution_copy, best_fit_coeffs);
    1367           0 :               Real best_fit_error = get_max_abs_value(solution_copy);
    1368             : 
    1369           0 :               if (best_fit_error > max_err)
    1370             :                 {
    1371           0 :                   max_err_index = training_index;
    1372           0 :                   max_err = best_fit_error;
    1373             :                 }
    1374           0 :             }
    1375           0 :           else if (get_rb_eim_evaluation().get_parametrized_function().on_mesh_nodes())
    1376             :             {
    1377             :               // Make a copy of the pre-computed solution for the specified training sample
    1378             :               // since we will modify it below to compute the best fit error.
    1379           0 :               NodeDataMap solution_copy = _local_node_parametrized_functions_for_training[training_index];
    1380             : 
    1381             :               // Perform an L2 projection in order to find the best approximation to
    1382             :               // the parametrized function from the current EIM space.
    1383           0 :               DenseVector<Number> best_fit_rhs(RB_size);
    1384           0 :               for (unsigned int i=0; i<RB_size; i++)
    1385             :                 {
    1386           0 :                   best_fit_rhs(i) = node_inner_product(solution_copy,
    1387           0 :                                                        get_rb_eim_evaluation().get_node_basis_function(i),
    1388             :                                                        /*apply_comp_scaling*/ false);
    1389             :                 }
    1390             : 
    1391             :               // Now compute the best fit by an LU solve
    1392           0 :               DenseMatrix<Number> RB_inner_product_matrix_N(RB_size);
    1393           0 :               _eim_projection_matrix.get_principal_submatrix(RB_size, RB_inner_product_matrix_N);
    1394             : 
    1395           0 :               DenseVector<Number> best_fit_coeffs;
    1396           0 :               RB_inner_product_matrix_N.lu_solve(best_fit_rhs, best_fit_coeffs);
    1397             : 
    1398           0 :               get_rb_eim_evaluation().node_decrement_vector(solution_copy, best_fit_coeffs);
    1399           0 :               Real best_fit_error = get_node_max_abs_value(solution_copy);
    1400             : 
    1401           0 :               if (best_fit_error > max_err)
    1402             :                 {
    1403           0 :                   max_err_index = training_index;
    1404           0 :                   max_err = best_fit_error;
    1405             :                 }
    1406           0 :             }
    1407             :           else
    1408             :             {
    1409             :               // Make a copy of the pre-computed solution for the specified training sample
    1410             :               // since we will modify it below to compute the best fit error.
    1411           0 :               QpDataMap solution_copy = _local_parametrized_functions_for_training[training_index];
    1412             : 
    1413             :               // Perform an L2 projection in order to find the best approximation to
    1414             :               // the parametrized function from the current EIM space.
    1415           0 :               DenseVector<Number> best_fit_rhs(RB_size);
    1416           0 :               for (unsigned int i=0; i<RB_size; i++)
    1417             :                 {
    1418           0 :                   best_fit_rhs(i) = inner_product(solution_copy,
    1419           0 :                                                   get_rb_eim_evaluation().get_basis_function(i),
    1420             :                                                   /*apply_comp_scaling*/ false);
    1421             :                 }
    1422             : 
    1423             :               // Now compute the best fit by an LU solve
    1424           0 :               DenseMatrix<Number> RB_inner_product_matrix_N(RB_size);
    1425           0 :               _eim_projection_matrix.get_principal_submatrix(RB_size, RB_inner_product_matrix_N);
    1426             : 
    1427           0 :               DenseVector<Number> best_fit_coeffs;
    1428           0 :               RB_inner_product_matrix_N.lu_solve(best_fit_rhs, best_fit_coeffs);
    1429             : 
    1430           0 :               get_rb_eim_evaluation().decrement_vector(solution_copy, best_fit_coeffs);
    1431           0 :               Real best_fit_error = get_max_abs_value(solution_copy);
    1432             : 
    1433           0 :               if (best_fit_error > max_err)
    1434             :                 {
    1435           0 :                   max_err_index = training_index;
    1436           0 :                   max_err = best_fit_error;
    1437             :                 }
    1438           0 :             }
    1439             :         }
    1440             :     }
    1441           0 :   else if(best_fit_type_flag == EIM_BEST_FIT)
    1442             :     {
    1443             :       // Perform EIM solve in order to find the approximation to solution
    1444             :       // (rb_eim_solve provides the EIM basis function coefficients used below)
    1445             : 
    1446           0 :       std::vector<RBParameters> training_parameters_copy(get_n_training_samples());
    1447           0 :       for (auto training_index : make_range(get_n_training_samples()))
    1448             :         {
    1449           0 :           training_parameters_copy[training_index] = get_params_from_training_set(training_index);
    1450             :         }
    1451             : 
    1452           0 :       get_rb_eim_evaluation().rb_eim_solves(training_parameters_copy, RB_size);
    1453           0 :       const std::vector<DenseVector<Number>> & rb_eim_solutions = get_rb_eim_evaluation().get_rb_eim_solutions();
    1454             : 
    1455           0 :       for (auto training_index : make_range(get_n_training_samples()))
    1456             :         {
    1457           0 :           const DenseVector<Number> & best_fit_coeffs = rb_eim_solutions[training_index];
    1458             : 
    1459           0 :           if (get_rb_eim_evaluation().get_parametrized_function().on_mesh_sides())
    1460             :             {
    1461           0 :               SideQpDataMap solution_copy = _local_side_parametrized_functions_for_training[training_index];
    1462           0 :               get_rb_eim_evaluation().side_decrement_vector(solution_copy, best_fit_coeffs);
    1463           0 :               Real best_fit_error = get_max_abs_value(solution_copy);
    1464             : 
    1465           0 :               if (best_fit_error > max_err)
    1466             :                 {
    1467           0 :                   max_err_index = training_index;
    1468           0 :                   max_err = best_fit_error;
    1469             :                 }
    1470             :             }
    1471           0 :           else if (get_rb_eim_evaluation().get_parametrized_function().on_mesh_nodes())
    1472             :             {
    1473           0 :               NodeDataMap solution_copy = _local_node_parametrized_functions_for_training[training_index];
    1474           0 :               get_rb_eim_evaluation().node_decrement_vector(solution_copy, best_fit_coeffs);
    1475           0 :               Real best_fit_error = get_node_max_abs_value(solution_copy);
    1476             : 
    1477           0 :               if (best_fit_error > max_err)
    1478             :                 {
    1479           0 :                   max_err_index = training_index;
    1480           0 :                   max_err = best_fit_error;
    1481             :                 }
    1482             :             }
    1483             :           else
    1484             :             {
    1485           0 :               QpDataMap solution_copy = _local_parametrized_functions_for_training[training_index];
    1486           0 :               get_rb_eim_evaluation().decrement_vector(solution_copy, best_fit_coeffs);
    1487           0 :               Real best_fit_error = get_max_abs_value(solution_copy);
    1488             : 
    1489           0 :               if (best_fit_error > max_err)
    1490             :                 {
    1491           0 :                   max_err_index = training_index;
    1492           0 :                   max_err = best_fit_error;
    1493             :                 }
    1494             :             }
    1495             :         }
    1496           0 :     }
    1497             :   else
    1498             :     {
    1499           0 :       libmesh_error_msg("EIM best fit type not recognized");
    1500             :     }
    1501             : 
    1502           0 :   return std::make_pair(max_err,max_err_index);
    1503             : }
    1504             : 
    1505           0 : void RBEIMConstruction::initialize_parametrized_functions_in_training_set()
    1506             : {
    1507           0 :   LOG_SCOPE("initialize_parametrized_functions_in_training_set()", "RBEIMConstruction");
    1508             : 
    1509           0 :   libmesh_error_msg_if(!serial_training_set,
    1510             :                        "Error: We must have serial_training_set==true in "
    1511             :                        "RBEIMConstruction::initialize_parametrized_functions_in_training_set");
    1512             : 
    1513           0 :   libMesh::out << "Initializing parametrized functions in training set..." << std::endl;
    1514             : 
    1515           0 :   RBEIMEvaluation & eim_eval = get_rb_eim_evaluation();
    1516             : 
    1517           0 :   if (eim_eval.get_parametrized_function().is_lookup_table)
    1518           0 :     eim_eval.get_parametrized_function().initialize_lookup_table();
    1519             : 
    1520             :   // Store the locations of all quadrature points
    1521           0 :   initialize_qp_data();
    1522             : 
    1523             :   // Keep track of the largest value in our parametrized functions
    1524             :   // in the training set. We can use this value for normalization
    1525             :   // purposes, for example.
    1526           0 :   _max_abs_value_in_training_set = 0.;
    1527             : 
    1528           0 :   unsigned int n_comps = eim_eval.get_parametrized_function().get_n_components();
    1529             : 
    1530             :   // Keep track of the maximum value per component. This will allow
    1531             :   // us to scale the components to all have a similar magnitude,
    1532             :   // which is helpful during the error assessment for the basis
    1533             :   // enrichment to ensure that components with smaller magnitude
    1534             :   // are not ignored.
    1535           0 :   std::vector<Real> max_abs_value_per_component_in_training_set(n_comps);
    1536             : 
    1537           0 :   if (eim_eval.get_parametrized_function().on_mesh_sides())
    1538             :     {
    1539           0 :       _local_side_parametrized_functions_for_training.resize( get_n_training_samples() );
    1540           0 :       for (auto i : make_range(get_n_training_samples()))
    1541             :         {
    1542           0 :           libMesh::out << "Initializing parametrized function for training sample "
    1543           0 :             << (i+1) << " of " << get_n_training_samples() << std::endl;
    1544             : 
    1545           0 :           set_params_from_training_set(i);
    1546             : 
    1547           0 :           eim_eval.get_parametrized_function().preevaluate_parametrized_function_on_mesh_sides(get_parameters(),
    1548           0 :                                                                                                _local_side_quad_point_locations,
    1549           0 :                                                                                                _local_side_quad_point_subdomain_ids,
    1550           0 :                                                                                                _local_side_quad_point_boundary_ids,
    1551           0 :                                                                                                _local_side_quad_point_side_types,
    1552           0 :                                                                                                _local_side_quad_point_locations_perturbations,
    1553           0 :                                                                                                *this);
    1554             : 
    1555           0 :           for (const auto & [elem_side_pair, xyz_vector] : _local_side_quad_point_locations)
    1556             :           {
    1557           0 :             std::vector<std::vector<Number>> comps_and_qps(n_comps);
    1558           0 :             for (unsigned int comp=0; comp<n_comps; comp++)
    1559             :               {
    1560           0 :                 comps_and_qps[comp].resize(xyz_vector.size());
    1561           0 :                 for (unsigned int qp : index_range(xyz_vector))
    1562             :                   {
    1563             :                     Number value =
    1564           0 :                       eim_eval.get_parametrized_function().lookup_preevaluated_side_value_on_mesh(comp,
    1565           0 :                                                                                                   elem_side_pair.first,
    1566           0 :                                                                                                   elem_side_pair.second,
    1567           0 :                                                                                                   qp);
    1568           0 :                     comps_and_qps[comp][qp] = value;
    1569             : 
    1570           0 :                     Real abs_value = std::abs(value);
    1571           0 :                     if (abs_value > _max_abs_value_in_training_set)
    1572             :                       {
    1573           0 :                         _max_abs_value_in_training_set = abs_value;
    1574           0 :                         _max_abs_value_in_training_set_index = i;
    1575             :                       }
    1576             : 
    1577           0 :                     if (abs_value > max_abs_value_per_component_in_training_set[comp])
    1578           0 :                       max_abs_value_per_component_in_training_set[comp] = abs_value;
    1579             :                   }
    1580             :               }
    1581             : 
    1582           0 :             _local_side_parametrized_functions_for_training[i][elem_side_pair] = comps_and_qps;
    1583           0 :           }
    1584             :         }
    1585             : 
    1586           0 :       libMesh::out << "Parametrized functions in training set initialized" << std::endl;
    1587             : 
    1588           0 :       unsigned int max_id = 0;
    1589           0 :       comm().maxloc(_max_abs_value_in_training_set, max_id);
    1590           0 :       comm().broadcast(_max_abs_value_in_training_set_index, max_id);
    1591           0 :       libMesh::out << "Maximum absolute value in the training set: "
    1592           0 :         << _max_abs_value_in_training_set << std::endl << std::endl;
    1593             : 
    1594             :       // Calculate the maximum value for each component in the training set
    1595             :       // across all components
    1596           0 :       comm().max(max_abs_value_per_component_in_training_set);
    1597             : 
    1598             :       // We store the maximum value across all components divided by the maximum value for this component
    1599             :       // so that when we scale using these factors all components should have a magnitude on the same
    1600             :       // order as the maximum component.
    1601           0 :       _component_scaling_in_training_set.resize(n_comps);
    1602           0 :       for (unsigned int i : make_range(n_comps))
    1603             :         {
    1604           0 :           if ((eim_eval.scale_components_in_enrichment().count(i) == 0) ||
    1605           0 :                max_abs_value_per_component_in_training_set[i] == 0.)
    1606           0 :             _component_scaling_in_training_set[i] = 1.;
    1607             :           else
    1608           0 :             _component_scaling_in_training_set[i] = _max_abs_value_in_training_set / max_abs_value_per_component_in_training_set[i];
    1609             :         }
    1610             :     }
    1611           0 :   else if (eim_eval.get_parametrized_function().on_mesh_nodes())
    1612             :     {
    1613           0 :       _local_node_parametrized_functions_for_training.resize( get_n_training_samples() );
    1614           0 :       for (auto i : make_range(get_n_training_samples()))
    1615             :         {
    1616           0 :           libMesh::out << "Initializing parametrized function for training sample "
    1617           0 :             << (i+1) << " of " << get_n_training_samples() << std::endl;
    1618             : 
    1619           0 :           set_params_from_training_set(i);
    1620             : 
    1621           0 :           eim_eval.get_parametrized_function().preevaluate_parametrized_function_on_mesh_nodes(get_parameters(),
    1622           0 :                                                                                                _local_node_locations,
    1623           0 :                                                                                                _local_node_boundary_ids,
    1624           0 :                                                                                                *this);
    1625             : 
    1626           0 :           for (const auto & pr : _local_node_locations)
    1627             :           {
    1628           0 :             const auto & node_id = pr.first;
    1629             : 
    1630           0 :             std::vector<Number> comps(n_comps);
    1631           0 :             for (unsigned int comp=0; comp<n_comps; comp++)
    1632             :               {
    1633             :                 Number value =
    1634           0 :                   eim_eval.get_parametrized_function().lookup_preevaluated_node_value_on_mesh(comp,
    1635           0 :                                                                                               node_id);
    1636           0 :                 comps[comp] = value;
    1637             : 
    1638           0 :                 Real abs_value = std::abs(value);
    1639           0 :                 if (abs_value > _max_abs_value_in_training_set)
    1640             :                   {
    1641           0 :                     _max_abs_value_in_training_set = abs_value;
    1642           0 :                     _max_abs_value_in_training_set_index = i;
    1643             :                   }
    1644             : 
    1645           0 :                 if (abs_value > max_abs_value_per_component_in_training_set[comp])
    1646           0 :                   max_abs_value_per_component_in_training_set[comp] = abs_value;
    1647             :               }
    1648             : 
    1649           0 :             _local_node_parametrized_functions_for_training[i][node_id] = comps;
    1650             :           }
    1651             :         }
    1652             : 
    1653           0 :       libMesh::out << "Parametrized functions in training set initialized" << std::endl;
    1654             : 
    1655           0 :       unsigned int max_id = 0;
    1656           0 :       comm().maxloc(_max_abs_value_in_training_set, max_id);
    1657           0 :       comm().broadcast(_max_abs_value_in_training_set_index, max_id);
    1658           0 :       libMesh::out << "Maximum absolute value in the training set: "
    1659           0 :         << _max_abs_value_in_training_set << std::endl << std::endl;
    1660             : 
    1661             :       // Calculate the maximum value for each component in the training set
    1662             :       // across all components
    1663           0 :       comm().max(max_abs_value_per_component_in_training_set);
    1664             : 
    1665             :       // We store the maximum value across all components divided by the maximum value for this component
    1666             :       // so that when we scale using these factors all components should have a magnitude on the same
    1667             :       // order as the maximum component.
    1668           0 :       _component_scaling_in_training_set.resize(n_comps);
    1669           0 :       for (unsigned int i : make_range(n_comps))
    1670             :         {
    1671           0 :           if ((eim_eval.scale_components_in_enrichment().count(i) == 0) ||
    1672           0 :                max_abs_value_per_component_in_training_set[i] == 0.)
    1673           0 :             _component_scaling_in_training_set[i] = 1.;
    1674             :           else
    1675           0 :             _component_scaling_in_training_set[i] = _max_abs_value_in_training_set / max_abs_value_per_component_in_training_set[i];
    1676             :         }
    1677             :     }
    1678             :   else
    1679             :     {
    1680           0 :       _local_parametrized_functions_for_training.resize( get_n_training_samples() );
    1681           0 :       for (auto i : make_range(get_n_training_samples()))
    1682             :         {
    1683           0 :           libMesh::out << "Initializing parametrized function for training sample "
    1684           0 :             << (i+1) << " of " << get_n_training_samples() << std::endl;
    1685             : 
    1686           0 :           set_params_from_training_set(i);
    1687             : 
    1688           0 :           eim_eval.get_parametrized_function().preevaluate_parametrized_function_on_mesh(get_parameters(),
    1689           0 :                                                                                         _local_quad_point_locations,
    1690           0 :                                                                                         _local_quad_point_subdomain_ids,
    1691           0 :                                                                                         _local_quad_point_locations_perturbations,
    1692           0 :                                                                                         *this);
    1693             : 
    1694           0 :           for (const auto & [elem_id, xyz_vector] : _local_quad_point_locations)
    1695             :           {
    1696           0 :             std::vector<std::vector<Number>> comps_and_qps(n_comps);
    1697           0 :             for (unsigned int comp=0; comp<n_comps; comp++)
    1698             :               {
    1699           0 :                 comps_and_qps[comp].resize(xyz_vector.size());
    1700           0 :                 for (unsigned int qp : index_range(xyz_vector))
    1701             :                   {
    1702             :                     Number value =
    1703           0 :                       eim_eval.get_parametrized_function().lookup_preevaluated_value_on_mesh(comp, elem_id, qp);
    1704           0 :                     comps_and_qps[comp][qp] = value;
    1705             : 
    1706           0 :                     Real abs_value = std::abs(value);
    1707           0 :                     if (abs_value > _max_abs_value_in_training_set)
    1708             :                       {
    1709           0 :                         _max_abs_value_in_training_set = abs_value;
    1710           0 :                         _max_abs_value_in_training_set_index = i;
    1711             :                       }
    1712             : 
    1713           0 :                     if (abs_value > max_abs_value_per_component_in_training_set[comp])
    1714           0 :                       max_abs_value_per_component_in_training_set[comp] = abs_value;
    1715             :                   }
    1716             :               }
    1717             : 
    1718           0 :             _local_parametrized_functions_for_training[i][elem_id] = comps_and_qps;
    1719           0 :           }
    1720             :         }
    1721             : 
    1722           0 :       libMesh::out << "Parametrized functions in training set initialized" << std::endl;
    1723             : 
    1724           0 :       unsigned int max_id = 0;
    1725           0 :       comm().maxloc(_max_abs_value_in_training_set, max_id);
    1726           0 :       comm().broadcast(_max_abs_value_in_training_set_index, max_id);
    1727           0 :       libMesh::out << "Maximum absolute value in the training set: "
    1728           0 :         << _max_abs_value_in_training_set << std::endl << std::endl;
    1729             : 
    1730             :       // Calculate the maximum value for each component in the training set
    1731             :       // across all components
    1732           0 :       comm().max(max_abs_value_per_component_in_training_set);
    1733             : 
    1734             :       // We store the maximum value across all components divided by the maximum value for this component
    1735             :       // so that when we scale using these factors all components should have a magnitude on the same
    1736             :       // order as the maximum component.
    1737           0 :       _component_scaling_in_training_set.resize(n_comps);
    1738           0 :       for (unsigned int i : make_range(n_comps))
    1739             :         {
    1740           0 :           if ((eim_eval.scale_components_in_enrichment().count(i) == 0) ||
    1741           0 :                max_abs_value_per_component_in_training_set[i] == 0.)
    1742           0 :             _component_scaling_in_training_set[i] = 1.;
    1743             :           else
    1744           0 :             _component_scaling_in_training_set[i] = _max_abs_value_in_training_set / max_abs_value_per_component_in_training_set[i];
    1745             :         }
    1746             :     }
    1747             :     // This function does nothing if rb_property_map from RBParametrizedFunction
    1748             :     // is empty which would result in an empty rb_property_map in VectorizedEvalInput
    1749             :     // stored in RBEIMEvaluation.
    1750           0 :     eim_eval.initialize_rb_property_map();
    1751           0 : }
    1752             : 
    1753           0 : void RBEIMConstruction::initialize_qp_data()
    1754             : {
    1755           0 :   LOG_SCOPE("initialize_qp_data()", "RBEIMConstruction");
    1756             : 
    1757           0 :   if (!get_rb_eim_evaluation().get_parametrized_function().requires_xyz_perturbations)
    1758             :     {
    1759           0 :       libMesh::out << "Initializing quadrature point locations" << std::endl;
    1760             :     }
    1761             :   else
    1762             :     {
    1763           0 :       libMesh::out << "Initializing quadrature point and perturbation locations" << std::endl;
    1764             :     }
    1765             : 
    1766             :   // Compute truth representation via L2 projection
    1767           0 :   const MeshBase & mesh = this->get_mesh();
    1768             : 
    1769           0 :   FEMContext context(*this);
    1770           0 :   init_context(context);
    1771             : 
    1772           0 :   if (get_rb_eim_evaluation().get_parametrized_function().on_mesh_sides())
    1773             :     {
    1774             :       const std::set<boundary_id_type> & parametrized_function_boundary_ids =
    1775           0 :         get_rb_eim_evaluation().get_parametrized_function().get_parametrized_function_boundary_ids();
    1776           0 :       libmesh_error_msg_if (parametrized_function_boundary_ids.empty(),
    1777             :                             "Need to have non-empty boundary IDs to initialize side data");
    1778             : 
    1779           0 :       _local_side_quad_point_locations.clear();
    1780           0 :       _local_side_quad_point_subdomain_ids.clear();
    1781           0 :       _local_side_quad_point_boundary_ids.clear();
    1782           0 :       _local_side_quad_point_JxW.clear();
    1783           0 :       _local_side_quad_point_side_types.clear();
    1784             : 
    1785           0 :       _local_side_quad_point_locations_perturbations.clear();
    1786             : 
    1787             :       // BoundaryInfo and related data structures
    1788           0 :       const auto & binfo = mesh.get_boundary_info();
    1789           0 :       std::vector<boundary_id_type> side_boundary_ids;
    1790             : 
    1791           0 :       for (const auto & elem : mesh.active_local_element_ptr_range())
    1792             :         {
    1793           0 :           dof_id_type elem_id = elem->id();
    1794             : 
    1795           0 :           context.pre_fe_reinit(*this, elem);
    1796             : 
    1797             :           // elem_fe is used for shellface data
    1798           0 :           auto elem_fe = context.get_element_fe(/*var=*/0, elem->dim());
    1799           0 :           const std::vector<Real> & JxW = elem_fe->get_JxW();
    1800           0 :           const std::vector<Point> & xyz = elem_fe->get_xyz();
    1801             : 
    1802             :           // side_fe is used for element side data
    1803           0 :           auto side_fe = context.get_side_fe(/*var=*/0, elem->dim());
    1804           0 :           const std::vector<Real> & JxW_side = side_fe->get_JxW();
    1805           0 :           const std::vector< Point > & xyz_side = side_fe->get_xyz();
    1806             : 
    1807           0 :           for (context.side = 0;
    1808           0 :                context.side != context.get_elem().n_sides();
    1809           0 :                ++context.side)
    1810             :             {
    1811             :               // skip non-boundary elements
    1812           0 :               if(!context.get_elem().neighbor_ptr(context.side))
    1813             :                 {
    1814           0 :                   binfo.boundary_ids(elem, context.side, side_boundary_ids);
    1815             : 
    1816           0 :                   bool has_side_boundary_id = false;
    1817           0 :                   boundary_id_type matching_boundary_id = BoundaryInfo::invalid_id;
    1818           0 :                   for (boundary_id_type side_boundary_id : side_boundary_ids)
    1819           0 :                     if(parametrized_function_boundary_ids.count(side_boundary_id))
    1820             :                       {
    1821           0 :                         has_side_boundary_id = true;
    1822           0 :                         matching_boundary_id = side_boundary_id;
    1823           0 :                         break;
    1824             :                       }
    1825             : 
    1826           0 :                   if(has_side_boundary_id)
    1827             :                   {
    1828           0 :                     context.get_side_fe(/*var=*/0, elem->dim())->reinit(elem, context.side);
    1829             : 
    1830           0 :                     auto elem_side_pair = std::make_pair(elem_id, context.side);
    1831             : 
    1832           0 :                     _local_side_quad_point_locations[elem_side_pair] = xyz_side;
    1833           0 :                     _local_side_quad_point_JxW[elem_side_pair] = JxW_side;
    1834           0 :                     _local_side_quad_point_subdomain_ids[elem_side_pair] = elem->subdomain_id();
    1835           0 :                     _local_side_quad_point_boundary_ids[elem_side_pair] = matching_boundary_id;
    1836             : 
    1837             :                     // This is a standard side (not a shellface) so set side type to 0
    1838           0 :                     _local_side_quad_point_side_types[elem_side_pair] = 0;
    1839             : 
    1840           0 :                     if (get_rb_eim_evaluation().get_parametrized_function().requires_xyz_perturbations)
    1841             :                       {
    1842           0 :                         Real fd_delta = get_rb_eim_evaluation().get_parametrized_function().fd_delta;
    1843             : 
    1844           0 :                         std::vector<std::vector<Point>> xyz_perturb_vec_at_qps;
    1845             : 
    1846           0 :                         for (const Point & xyz_qp : xyz_side)
    1847             :                           {
    1848           0 :                             std::vector<Point> xyz_perturb_vec;
    1849           0 :                             if (elem->dim() == 3)
    1850             :                               {
    1851             :                                 // In this case we have a 3D element, and hence the side is 2D.
    1852             :                                 //
    1853             :                                 // We use the following approach to perturb xyz:
    1854             :                                 //  1) inverse map xyz to the reference element
    1855             :                                 //  2) perturb on the reference element in the (xi,eta) "directions"
    1856             :                                 //  3) map the perturbed points back to the physical element
    1857             :                                 // This approach is necessary to ensure that the perturbed points
    1858             :                                 // are still in the element's side.
    1859             : 
    1860           0 :                                 std::unique_ptr<const Elem> elem_side;
    1861           0 :                                 elem->build_side_ptr(elem_side, context.side);
    1862             : 
    1863             :                                 Point xi_eta =
    1864           0 :                                   FEMap::inverse_map(elem_side->dim(),
    1865             :                                                      elem_side.get(),
    1866             :                                                      xyz_qp,
    1867             :                                                      /*Newton iteration tolerance*/ TOLERANCE,
    1868           0 :                                                      /*secure*/ true);
    1869             : 
    1870             :                                 // Inverse map should map back to a 2D reference domain
    1871           0 :                                 libmesh_assert(std::abs(xi_eta(2)) < TOLERANCE);
    1872             : 
    1873           0 :                                 Point xi_eta_perturb = xi_eta;
    1874             : 
    1875           0 :                                 xi_eta_perturb(0) += fd_delta;
    1876             :                                 Point xyz_perturb_0 =
    1877           0 :                                   FEMap::map(elem_side->dim(),
    1878             :                                              elem_side.get(),
    1879           0 :                                              xi_eta_perturb);
    1880           0 :                                 xi_eta_perturb(0) -= fd_delta;
    1881             : 
    1882           0 :                                 xi_eta_perturb(1) += fd_delta;
    1883             :                                 Point xyz_perturb_1 =
    1884           0 :                                   FEMap::map(elem_side->dim(),
    1885             :                                              elem_side.get(),
    1886           0 :                                              xi_eta_perturb);
    1887           0 :                                 xi_eta_perturb(1) -= fd_delta;
    1888             : 
    1889             :                                 // Finally, we rescale xyz_perturb_0 and xyz_perturb_1 so that
    1890             :                                 // (xyz_perturb - xyz_qp).norm() == fd_delta, since this is
    1891             :                                 // required in order to compute finite differences correctly.
    1892           0 :                                 Point unit_0 = (xyz_perturb_0-xyz_qp).unit();
    1893           0 :                                 Point unit_1 = (xyz_perturb_1-xyz_qp).unit();
    1894             : 
    1895           0 :                                 xyz_perturb_vec.emplace_back(xyz_qp + fd_delta*unit_0);
    1896           0 :                                 xyz_perturb_vec.emplace_back(xyz_qp + fd_delta*unit_1);
    1897           0 :                               }
    1898             :                             else
    1899             :                               {
    1900             :                                 // We current do nothing for sides of dim=2 or dim=1 elements
    1901             :                                 // since we have no need for this capability so far.
    1902             :                                 // Support for these cases could be added if it is needed.
    1903             :                               }
    1904             : 
    1905           0 :                             xyz_perturb_vec_at_qps.emplace_back(xyz_perturb_vec);
    1906             :                           }
    1907             : 
    1908           0 :                         _local_side_quad_point_locations_perturbations[elem_side_pair] = xyz_perturb_vec_at_qps;
    1909           0 :                       }
    1910             :                   }
    1911             :                 }
    1912             :             }
    1913             : 
    1914             :             // In the case of 2D elements, we also check the shellfaces
    1915           0 :             if (elem->dim() == 2)
    1916           0 :               for (unsigned int shellface_index=0; shellface_index<2; shellface_index++)
    1917             :                 {
    1918           0 :                   binfo.shellface_boundary_ids(elem, shellface_index, side_boundary_ids);
    1919             : 
    1920           0 :                   bool has_side_boundary_id = false;
    1921           0 :                   boundary_id_type matching_boundary_id = BoundaryInfo::invalid_id;
    1922           0 :                   for (boundary_id_type side_boundary_id : side_boundary_ids)
    1923           0 :                     if(parametrized_function_boundary_ids.count(side_boundary_id))
    1924             :                       {
    1925           0 :                         has_side_boundary_id = true;
    1926           0 :                         matching_boundary_id = side_boundary_id;
    1927           0 :                         break;
    1928             :                       }
    1929             : 
    1930           0 :                   if(has_side_boundary_id)
    1931             :                   {
    1932           0 :                     context.elem_fe_reinit();
    1933             : 
    1934             :                     // We use shellface_index as the side_index since shellface boundary conditions
    1935             :                     // are stored separately from side boundary conditions in BoundaryInfo.
    1936           0 :                     auto elem_side_pair = std::make_pair(elem_id, shellface_index);
    1937             : 
    1938           0 :                     _local_side_quad_point_locations[elem_side_pair] = xyz;
    1939           0 :                     _local_side_quad_point_JxW[elem_side_pair] = JxW;
    1940           0 :                     _local_side_quad_point_subdomain_ids[elem_side_pair] = elem->subdomain_id();
    1941           0 :                     _local_side_quad_point_boundary_ids[elem_side_pair] = matching_boundary_id;
    1942             : 
    1943             :                     // This is a shellface (not a standard side) so set side type to 1
    1944           0 :                     _local_side_quad_point_side_types[elem_side_pair] = 1;
    1945             : 
    1946           0 :                     if (get_rb_eim_evaluation().get_parametrized_function().requires_xyz_perturbations)
    1947             :                       {
    1948           0 :                         Real fd_delta = get_rb_eim_evaluation().get_parametrized_function().fd_delta;
    1949             : 
    1950           0 :                         std::vector<std::vector<Point>> xyz_perturb_vec_at_qps;
    1951             : 
    1952           0 :                         for (const Point & xyz_qp : xyz)
    1953             :                           {
    1954           0 :                             std::vector<Point> xyz_perturb_vec;
    1955             :                             // Here we follow the same approach as above for getting xyz_perturb_vec,
    1956             :                             // except that we are using the element itself instead of its side.
    1957             :                             {
    1958             :                               Point xi_eta =
    1959           0 :                                 FEMap::inverse_map(elem->dim(),
    1960             :                                                    elem,
    1961             :                                                    xyz_qp,
    1962             :                                                    /*Newton iteration tolerance*/ TOLERANCE,
    1963           0 :                                                    /*secure*/ true);
    1964             : 
    1965             :                               // Inverse map should map back to a 2D reference domain
    1966           0 :                               libmesh_assert(std::abs(xi_eta(2)) < TOLERANCE);
    1967             : 
    1968           0 :                               Point xi_eta_perturb = xi_eta;
    1969             : 
    1970           0 :                               xi_eta_perturb(0) += fd_delta;
    1971             :                               Point xyz_perturb_0 =
    1972           0 :                                 FEMap::map(elem->dim(),
    1973             :                                             elem,
    1974           0 :                                             xi_eta_perturb);
    1975           0 :                               xi_eta_perturb(0) -= fd_delta;
    1976             : 
    1977           0 :                               xi_eta_perturb(1) += fd_delta;
    1978             :                               Point xyz_perturb_1 =
    1979           0 :                                 FEMap::map(elem->dim(),
    1980             :                                             elem,
    1981           0 :                                             xi_eta_perturb);
    1982           0 :                               xi_eta_perturb(1) -= fd_delta;
    1983             : 
    1984             :                               // Finally, we rescale xyz_perturb_0 and xyz_perturb_1 so that
    1985             :                               // (xyz_perturb - xyz_qp).norm() == fd_delta, since this is
    1986             :                               // required in order to compute finite differences correctly.
    1987           0 :                               Point unit_0 = (xyz_perturb_0-xyz_qp).unit();
    1988           0 :                               Point unit_1 = (xyz_perturb_1-xyz_qp).unit();
    1989             : 
    1990           0 :                               xyz_perturb_vec.emplace_back(xyz_qp + fd_delta*unit_0);
    1991           0 :                               xyz_perturb_vec.emplace_back(xyz_qp + fd_delta*unit_1);
    1992             :                             }
    1993             : 
    1994           0 :                             xyz_perturb_vec_at_qps.emplace_back(xyz_perturb_vec);
    1995             :                           }
    1996             : 
    1997           0 :                         _local_side_quad_point_locations_perturbations[elem_side_pair] = xyz_perturb_vec_at_qps;
    1998           0 :                       }
    1999             :                   }
    2000             :                 }
    2001           0 :         }
    2002             :     }
    2003           0 :   else if (get_rb_eim_evaluation().get_parametrized_function().on_mesh_nodes())
    2004             :     {
    2005             :       const std::set<boundary_id_type> & parametrized_function_boundary_ids =
    2006           0 :         get_rb_eim_evaluation().get_parametrized_function().get_parametrized_function_boundary_ids();
    2007           0 :       libmesh_error_msg_if (parametrized_function_boundary_ids.empty(),
    2008             :                             "Need to have non-empty boundary IDs to initialize node data");
    2009             : 
    2010           0 :       _local_node_locations.clear();
    2011           0 :       _local_node_boundary_ids.clear();
    2012             : 
    2013           0 :       const auto & binfo = mesh.get_boundary_info();
    2014             : 
    2015             :       // Make a set with all the nodes that have nodesets. Use
    2016             :       // a set so that we don't have any duplicate entries. We
    2017             :       // deal with duplicate entries below by getting all boundary
    2018             :       // IDs on each node.
    2019           0 :       std::set<dof_id_type> nodes_with_nodesets;
    2020           0 :       for (const auto & t : binfo.build_node_list())
    2021           0 :         nodes_with_nodesets.insert(std::get<0>(t));
    2022             : 
    2023             :       // To be filled in by BoundaryInfo calls in loop below
    2024           0 :       std::vector<boundary_id_type> node_boundary_ids;
    2025             : 
    2026           0 :       for (dof_id_type node_id : nodes_with_nodesets)
    2027             :         {
    2028           0 :           const Node * node = mesh.node_ptr(node_id);
    2029             : 
    2030           0 :           if (node->processor_id() != mesh.comm().rank())
    2031           0 :             continue;
    2032             : 
    2033           0 :           binfo.boundary_ids(node, node_boundary_ids);
    2034             : 
    2035           0 :           bool has_node_boundary_id = false;
    2036           0 :           boundary_id_type matching_boundary_id = BoundaryInfo::invalid_id;
    2037           0 :           for (boundary_id_type node_boundary_id : node_boundary_ids)
    2038           0 :             if(parametrized_function_boundary_ids.count(node_boundary_id))
    2039             :               {
    2040           0 :                 has_node_boundary_id = true;
    2041           0 :                 matching_boundary_id = node_boundary_id;
    2042           0 :                 break;
    2043             :               }
    2044             : 
    2045           0 :           if(has_node_boundary_id)
    2046             :             {
    2047           0 :               _local_node_locations[node_id] = *node;
    2048           0 :               _local_node_boundary_ids[node_id] = matching_boundary_id;
    2049             :             }
    2050             :         }
    2051             :     }
    2052             :   else
    2053             :     {
    2054           0 :       _local_quad_point_locations.clear();
    2055           0 :       _local_quad_point_subdomain_ids.clear();
    2056           0 :       _local_quad_point_JxW.clear();
    2057             : 
    2058           0 :       _local_quad_point_locations_perturbations.clear();
    2059             : 
    2060           0 :       for (const auto & elem : mesh.active_local_element_ptr_range())
    2061             :         {
    2062           0 :           auto elem_fe = context.get_element_fe(/*var=*/0, elem->dim());
    2063           0 :           const std::vector<Real> & JxW = elem_fe->get_JxW();
    2064           0 :           const std::vector<Point> & xyz = elem_fe->get_xyz();
    2065             : 
    2066           0 :           dof_id_type elem_id = elem->id();
    2067             : 
    2068           0 :           context.pre_fe_reinit(*this, elem);
    2069           0 :           context.elem_fe_reinit();
    2070             : 
    2071           0 :           _local_quad_point_locations[elem_id] = xyz;
    2072           0 :           _local_quad_point_JxW[elem_id] = JxW;
    2073           0 :           _local_quad_point_subdomain_ids[elem_id] = elem->subdomain_id();
    2074             : 
    2075           0 :           if (get_rb_eim_evaluation().get_parametrized_function().requires_xyz_perturbations)
    2076             :             {
    2077           0 :               Real fd_delta = get_rb_eim_evaluation().get_parametrized_function().fd_delta;
    2078             : 
    2079           0 :               std::vector<std::vector<Point>> xyz_perturb_vec_at_qps;
    2080             : 
    2081           0 :               for (const Point & xyz_qp : xyz)
    2082             :                 {
    2083           0 :                   std::vector<Point> xyz_perturb_vec;
    2084           0 :                   if (elem->dim() == 3)
    2085             :                     {
    2086           0 :                       Point xyz_perturb = xyz_qp;
    2087             : 
    2088           0 :                       xyz_perturb(0) += fd_delta;
    2089           0 :                       xyz_perturb_vec.emplace_back(xyz_perturb);
    2090           0 :                       xyz_perturb(0) -= fd_delta;
    2091             : 
    2092           0 :                       xyz_perturb(1) += fd_delta;
    2093           0 :                       xyz_perturb_vec.emplace_back(xyz_perturb);
    2094           0 :                       xyz_perturb(1) -= fd_delta;
    2095             : 
    2096           0 :                       xyz_perturb(2) += fd_delta;
    2097           0 :                       xyz_perturb_vec.emplace_back(xyz_perturb);
    2098           0 :                       xyz_perturb(2) -= fd_delta;
    2099             :                     }
    2100           0 :                   else if (elem->dim() == 2)
    2101             :                     {
    2102             :                       // In this case we assume that we have a 2D element
    2103             :                       // embedded in 3D space. In this case we have to use
    2104             :                       // the following approach to perturb xyz:
    2105             :                       //  1) inverse map xyz to the reference element
    2106             :                       //  2) perturb on the reference element in the (xi,eta) "directions"
    2107             :                       //  3) map the perturbed points back to the physical element
    2108             :                       // This approach is necessary to ensure that the perturbed points
    2109             :                       // are still in the element.
    2110             : 
    2111             :                       Point xi_eta =
    2112           0 :                         FEMap::inverse_map(elem->dim(),
    2113             :                                           elem,
    2114             :                                           xyz_qp,
    2115             :                                           /*Newton iteration tolerance*/ TOLERANCE,
    2116           0 :                                           /*secure*/ true);
    2117             : 
    2118             :                       // Inverse map should map back to a 2D reference domain
    2119           0 :                       libmesh_assert(std::abs(xi_eta(2)) < TOLERANCE);
    2120             : 
    2121           0 :                       Point xi_eta_perturb = xi_eta;
    2122             : 
    2123           0 :                       xi_eta_perturb(0) += fd_delta;
    2124             :                       Point xyz_perturb_0 =
    2125           0 :                         FEMap::map(elem->dim(),
    2126             :                                   elem,
    2127           0 :                                   xi_eta_perturb);
    2128           0 :                       xi_eta_perturb(0) -= fd_delta;
    2129             : 
    2130           0 :                       xi_eta_perturb(1) += fd_delta;
    2131             :                       Point xyz_perturb_1 =
    2132           0 :                         FEMap::map(elem->dim(),
    2133             :                                   elem,
    2134           0 :                                   xi_eta_perturb);
    2135           0 :                       xi_eta_perturb(1) -= fd_delta;
    2136             : 
    2137             :                       // Finally, we rescale xyz_perturb_0 and xyz_perturb_1 so that
    2138             :                       // (xyz_perturb - xyz_qp).norm() == fd_delta, since this is
    2139             :                       // required in order to compute finite differences correctly.
    2140           0 :                       Point unit_0 = (xyz_perturb_0-xyz_qp).unit();
    2141           0 :                       Point unit_1 = (xyz_perturb_1-xyz_qp).unit();
    2142             : 
    2143           0 :                       xyz_perturb_vec.emplace_back(xyz_qp + fd_delta*unit_0);
    2144           0 :                       xyz_perturb_vec.emplace_back(xyz_qp + fd_delta*unit_1);
    2145             :                     }
    2146             :                   else
    2147             :                     {
    2148             :                       // We current do nothing in the dim=1 case since
    2149             :                       // we have no need for this capability so far.
    2150             :                       // Support for this case could be added if it is
    2151             :                       // needed.
    2152             :                     }
    2153             : 
    2154           0 :                   xyz_perturb_vec_at_qps.emplace_back(xyz_perturb_vec);
    2155             :                 }
    2156             : 
    2157           0 :               _local_quad_point_locations_perturbations[elem_id] = xyz_perturb_vec_at_qps;
    2158           0 :             }
    2159           0 :         }
    2160             :     }
    2161           0 : }
    2162             : 
    2163             : Number
    2164           0 : RBEIMConstruction::inner_product(const QpDataMap & v, const QpDataMap & w, bool apply_comp_scaling)
    2165             : {
    2166           0 :   LOG_SCOPE("inner_product()", "RBEIMConstruction");
    2167             : 
    2168           0 :   Number val = 0.;
    2169             : 
    2170           0 :   for (const auto & [elem_id, v_comp_and_qp] : v)
    2171             :     {
    2172           0 :       const auto & w_comp_and_qp = libmesh_map_find(w, elem_id);
    2173           0 :       const auto & JxW = libmesh_map_find(_local_quad_point_JxW, elem_id);
    2174             : 
    2175           0 :       for (const auto & comp : index_range(v_comp_and_qp))
    2176             :         {
    2177           0 :           const std::vector<Number> & v_qp = v_comp_and_qp[comp];
    2178           0 :           const std::vector<Number> & w_qp = w_comp_and_qp[comp];
    2179             : 
    2180           0 :           Real comp_scaling = 1.;
    2181           0 :           if (apply_comp_scaling)
    2182             :             {
    2183             :               // We square the component scaling here because it occurs twice in
    2184             :               // the inner product calculation below.
    2185           0 :               comp_scaling = std::pow(_component_scaling_in_training_set[comp], 2.);
    2186             :             }
    2187             : 
    2188           0 :           for (unsigned int qp : index_range(JxW))
    2189           0 :             val += JxW[qp] * comp_scaling * v_qp[qp] * libmesh_conj(w_qp[qp]);
    2190             :         }
    2191             :     }
    2192             : 
    2193           0 :   comm().sum(val);
    2194           0 :   return val;
    2195             : }
    2196             : 
    2197             : Number
    2198           0 : RBEIMConstruction::side_inner_product(const SideQpDataMap & v, const SideQpDataMap & w, bool apply_comp_scaling)
    2199             : {
    2200           0 :   LOG_SCOPE("side_inner_product()", "RBEIMConstruction");
    2201             : 
    2202           0 :   Number val = 0.;
    2203             : 
    2204           0 :   for (const auto & [elem_and_side, v_comp_and_qp] : v)
    2205             :     {
    2206           0 :       const auto & w_comp_and_qp = libmesh_map_find(w, elem_and_side);
    2207           0 :       const auto & JxW = libmesh_map_find(_local_side_quad_point_JxW, elem_and_side);
    2208             : 
    2209           0 :       for (const auto & comp : index_range(v_comp_and_qp))
    2210             :         {
    2211           0 :           const std::vector<Number> & v_qp = v_comp_and_qp[comp];
    2212           0 :           const std::vector<Number> & w_qp = w_comp_and_qp[comp];
    2213             : 
    2214           0 :           Real comp_scaling = 1.;
    2215           0 :           if (apply_comp_scaling)
    2216             :             {
    2217             :               // We square the component scaling here because it occurs twice in
    2218             :               // the inner product calculation below.
    2219           0 :               comp_scaling = std::pow(_component_scaling_in_training_set[comp], 2.);
    2220             :             }
    2221             : 
    2222           0 :           for (unsigned int qp : index_range(JxW))
    2223           0 :             val += JxW[qp] * comp_scaling * v_qp[qp] * libmesh_conj(w_qp[qp]);
    2224             :         }
    2225             :     }
    2226             : 
    2227           0 :   comm().sum(val);
    2228           0 :   return val;
    2229             : }
    2230             : 
    2231             : Number
    2232           0 : RBEIMConstruction::node_inner_product(const NodeDataMap & v, const NodeDataMap & w, bool apply_comp_scaling)
    2233             : {
    2234           0 :   LOG_SCOPE("node_inner_product()", "RBEIMConstruction");
    2235             : 
    2236           0 :   Number val = 0.;
    2237             : 
    2238           0 :   for (const auto & [node_id, v_comps] : v)
    2239             :     {
    2240           0 :       const auto & w_comps = libmesh_map_find(w, node_id);
    2241             : 
    2242           0 :       for (const auto & comp : index_range(v_comps))
    2243             :         {
    2244             :           // There is no quadrature rule on nodes, so we just multiply the values directly.
    2245             :           // Hence we effectively work with the Euclidean inner product in this case.
    2246             : 
    2247           0 :           Real comp_scaling = 1.;
    2248           0 :           if (apply_comp_scaling)
    2249             :             {
    2250             :               // We square the component scaling here because it occurs twice in
    2251             :               // the inner product calculation below.
    2252           0 :               comp_scaling = std::pow(_component_scaling_in_training_set[comp], 2.);
    2253             :             }
    2254             : 
    2255           0 :           val += comp_scaling * v_comps[comp] * libmesh_conj(w_comps[comp]);
    2256             :         }
    2257             :     }
    2258             : 
    2259           0 :   comm().sum(val);
    2260           0 :   return val;
    2261             : }
    2262             : 
    2263           0 : Real RBEIMConstruction::get_node_max_abs_value(const NodeDataMap & v) const
    2264             : {
    2265           0 :   Real max_value = 0.;
    2266             : 
    2267           0 :   for (const auto & pr : v)
    2268             :     {
    2269           0 :       const auto & values = pr.second;
    2270           0 :       for (const auto & comp : index_range(values))
    2271             :         {
    2272           0 :           const auto & value = values[comp];
    2273             : 
    2274           0 :           Real comp_scaling = 1.;
    2275           0 :           if (get_rb_eim_evaluation().scale_components_in_enrichment().count(comp))
    2276             :             {
    2277             :               // Make sure that _component_scaling_in_training_set is initialized
    2278           0 :               libmesh_error_msg_if(comp >= _component_scaling_in_training_set.size(),
    2279             :                                   "Invalid vector index");
    2280           0 :               comp_scaling = _component_scaling_in_training_set[comp];
    2281             :             }
    2282             : 
    2283           0 :           max_value = std::max(max_value, std::abs(value * comp_scaling));
    2284             :         }
    2285             :     }
    2286             : 
    2287           0 :   comm().max(max_value);
    2288           0 :   return max_value;
    2289             : }
    2290             : 
    2291           0 : void RBEIMConstruction::enrich_eim_approximation(unsigned int training_index,
    2292             :                                                  bool add_basis_function,
    2293             :                                                  EimPointData * eim_point_data)
    2294             : {
    2295           0 :   LOG_SCOPE("enrich_eim_approximation()", "RBEIMConstruction");
    2296             : 
    2297           0 :   RBEIMEvaluation & eim_eval = get_rb_eim_evaluation();
    2298             : 
    2299           0 :   set_params_from_training_set(training_index);
    2300             : 
    2301           0 :   if (eim_eval.get_parametrized_function().on_mesh_sides())
    2302           0 :     enrich_eim_approximation_on_sides(_local_side_parametrized_functions_for_training[training_index],
    2303             :                                       add_basis_function,
    2304             :                                       eim_point_data);
    2305           0 :   else if (eim_eval.get_parametrized_function().on_mesh_nodes())
    2306           0 :     enrich_eim_approximation_on_nodes(_local_node_parametrized_functions_for_training[training_index],
    2307             :                                       add_basis_function,
    2308             :                                       eim_point_data);
    2309             :   else
    2310             :     {
    2311           0 :       enrich_eim_approximation_on_interiors(_local_parametrized_functions_for_training[training_index],
    2312             :                                             add_basis_function,
    2313             :                                             eim_point_data);
    2314             :     }
    2315           0 : }
    2316             : 
    2317           0 : bool RBEIMConstruction::enrich_eim_approximation_on_sides(const SideQpDataMap & side_pf,
    2318             :                                                           bool add_basis_function,
    2319             :                                                           EimPointData * eim_point_data)
    2320             : {
    2321             :   // Make a copy of the input parametrized function, since we will modify this below
    2322             :   // to give us a new basis function.
    2323           0 :   SideQpDataMap local_pf = side_pf;
    2324             : 
    2325           0 :   RBEIMEvaluation & eim_eval = get_rb_eim_evaluation();
    2326             : 
    2327             :   // If we have at least one basis function, then we need to use
    2328             :   // rb_eim_solve() to find the EIM interpolation error. Otherwise,
    2329             :   // just use solution as is.
    2330           0 :   if (!eim_point_data && (eim_eval.get_n_basis_functions() > 0))
    2331             :     {
    2332             :       // Get the right-hand side vector for the EIM approximation
    2333             :       // by sampling the parametrized function (stored in solution)
    2334             :       // at the interpolation points.
    2335           0 :       unsigned int RB_size = eim_eval.get_n_basis_functions();
    2336           0 :       DenseVector<Number> EIM_rhs(RB_size);
    2337           0 :       for (unsigned int i=0; i<RB_size; i++)
    2338             :         {
    2339           0 :           EIM_rhs(i) =
    2340           0 :             RBEIMEvaluation::get_parametrized_function_side_value(comm(),
    2341             :                                                                   local_pf,
    2342             :                                                                   eim_eval.get_interpolation_points_elem_id(i),
    2343             :                                                                   eim_eval.get_interpolation_points_side_index(i),
    2344             :                                                                   eim_eval.get_interpolation_points_comp(i),
    2345             :                                                                   eim_eval.get_interpolation_points_qp(i));
    2346             :         }
    2347             : 
    2348           0 :       eim_eval.set_parameters( get_parameters() );
    2349           0 :       DenseVector<Number> rb_eim_solution = eim_eval.rb_eim_solve(EIM_rhs);
    2350             : 
    2351             :       // Load the "EIM residual" into solution by subtracting
    2352             :       // the EIM approximation
    2353           0 :       eim_eval.side_decrement_vector(local_pf, rb_eim_solution);
    2354             :     }
    2355             : 
    2356             :   // Find the quadrature point at which local_pf (which now stores
    2357             :   // the "EIM residual") has maximum absolute value
    2358           0 :   Number optimal_value = 0.;
    2359           0 :   Point optimal_point;
    2360           0 :   unsigned int optimal_comp = 0;
    2361           0 :   dof_id_type optimal_elem_id = DofObject::invalid_id;
    2362           0 :   unsigned int optimal_side_index = 0;
    2363           0 :   subdomain_id_type optimal_subdomain_id = 0;
    2364           0 :   boundary_id_type optimal_boundary_id = 0;
    2365           0 :   unsigned int optimal_qp = 0;
    2366           0 :   std::vector<Point> optimal_point_perturbs;
    2367           0 :   std::vector<Real> optimal_point_phi_i_qp;
    2368             : 
    2369             :   // Initialize largest_abs_value to be negative so that it definitely gets updated.
    2370           0 :   Real largest_abs_value = -1.;
    2371             : 
    2372             :   // In order to compute phi_i_qp, we initialize a FEMContext
    2373           0 :   FEMContext con(*this);
    2374           0 :   init_context(con);
    2375             : 
    2376           0 :   for (const auto & [elem_and_side, comp_and_qp] : local_pf)
    2377             :     {
    2378           0 :       dof_id_type elem_id = elem_and_side.first;
    2379           0 :       unsigned int side_index = elem_and_side.second;
    2380             : 
    2381           0 :       const Elem & elem_ref = get_mesh().elem_ref(elem_id);
    2382           0 :       con.pre_fe_reinit(*this, &elem_ref);
    2383             : 
    2384           0 :       unsigned int side_type = libmesh_map_find(_local_side_quad_point_side_types, elem_and_side);
    2385             : 
    2386           0 :       std::vector<std::vector<Real>> phi;
    2387             :       // side_type == 0 --> standard side
    2388             :       // side_type == 1 --> shellface
    2389           0 :       if (side_type == 0)
    2390             :         {
    2391             :           // TODO: We only want the "dofs on side" entries
    2392             :           // from phi_side. Could do this by initing an FE object
    2393             :           // on the side itself, rather than using get_side_fe().
    2394           0 :           auto side_fe = con.get_side_fe(/*var=*/ 0);
    2395           0 :           side_fe->reinit(&elem_ref, side_index);
    2396             : 
    2397           0 :           phi = side_fe->get_phi();
    2398             :         }
    2399           0 :       else if (side_type == 1)
    2400             :         {
    2401           0 :           con.elem_fe_reinit();
    2402             : 
    2403           0 :           auto elem_fe = con.get_element_fe(/*var=*/0, elem_ref.dim());
    2404           0 :           phi = elem_fe->get_phi();
    2405             :         }
    2406             :       else
    2407           0 :         libmesh_error_msg ("Unrecognized side_type: " << side_type);
    2408             : 
    2409           0 :       for (const auto & comp : index_range(comp_and_qp))
    2410             :         {
    2411           0 :           const std::vector<Number> & qp_values = comp_and_qp[comp];
    2412             : 
    2413           0 :           for (auto qp : index_range(qp_values))
    2414             :             {
    2415           0 :               Number value = qp_values[qp];
    2416           0 :               Real abs_value = std::abs(value);
    2417             : 
    2418           0 :               bool update_optimal_point = false;
    2419           0 :               if (!eim_point_data)
    2420           0 :                 update_optimal_point = (abs_value > largest_abs_value);
    2421             :               else
    2422           0 :                 update_optimal_point = (elem_id == eim_point_data->elem_id) &&
    2423           0 :                                        (side_index == eim_point_data->side_index) &&
    2424           0 :                                        (comp == eim_point_data->comp_index) &&
    2425           0 :                                        (qp == eim_point_data->qp_index);
    2426             : 
    2427           0 :               if (update_optimal_point)
    2428             :                 {
    2429           0 :                   largest_abs_value = abs_value;
    2430           0 :                   optimal_value = value;
    2431           0 :                   optimal_comp = comp;
    2432           0 :                   optimal_elem_id = elem_id;
    2433           0 :                   optimal_side_index = side_index;
    2434           0 :                   optimal_qp = qp;
    2435             : 
    2436           0 :                   optimal_point_phi_i_qp.resize(phi.size());
    2437           0 :                   for (auto i : index_range(phi))
    2438           0 :                     optimal_point_phi_i_qp[i] = phi[i][qp];
    2439             : 
    2440             :                   const auto & point_list =
    2441           0 :                     libmesh_map_find(_local_side_quad_point_locations, elem_and_side);
    2442             : 
    2443           0 :                   libmesh_error_msg_if(qp >= point_list.size(), "Error: Invalid qp");
    2444             : 
    2445           0 :                   optimal_point = point_list[qp];
    2446             : 
    2447           0 :                   optimal_subdomain_id = libmesh_map_find(_local_side_quad_point_subdomain_ids, elem_and_side);
    2448           0 :                   optimal_boundary_id = libmesh_map_find(_local_side_quad_point_boundary_ids, elem_and_side);
    2449             : 
    2450           0 :                   if (get_rb_eim_evaluation().get_parametrized_function().requires_xyz_perturbations)
    2451             :                     {
    2452             :                       const auto & perturb_list =
    2453           0 :                         libmesh_map_find(_local_side_quad_point_locations_perturbations, elem_and_side);
    2454             : 
    2455           0 :                       libmesh_error_msg_if(qp >= perturb_list.size(), "Error: Invalid qp");
    2456             : 
    2457           0 :                       optimal_point_perturbs = perturb_list[qp];
    2458             :                     }
    2459             :                 }
    2460             :             }
    2461             :         }
    2462           0 :     }
    2463             : 
    2464             :   // Find out which processor has the largest of the abs values
    2465             :   // and broadcast from that processor.
    2466             :   unsigned int proc_ID_index;
    2467           0 :   this->comm().maxloc(largest_abs_value, proc_ID_index);
    2468             : 
    2469           0 :   this->comm().broadcast(optimal_value, proc_ID_index);
    2470           0 :   this->comm().broadcast(optimal_point, proc_ID_index);
    2471           0 :   this->comm().broadcast(optimal_comp, proc_ID_index);
    2472           0 :   this->comm().broadcast(optimal_elem_id, proc_ID_index);
    2473           0 :   this->comm().broadcast(optimal_side_index, proc_ID_index);
    2474           0 :   this->comm().broadcast(optimal_subdomain_id, proc_ID_index);
    2475           0 :   this->comm().broadcast(optimal_boundary_id, proc_ID_index);
    2476           0 :   this->comm().broadcast(optimal_qp, proc_ID_index);
    2477           0 :   this->comm().broadcast(optimal_point_perturbs, proc_ID_index);
    2478           0 :   this->comm().broadcast(optimal_point_phi_i_qp, proc_ID_index);
    2479             : 
    2480           0 :   libmesh_error_msg_if(optimal_elem_id == DofObject::invalid_id, "Error: Invalid element ID");
    2481             : 
    2482           0 :   if (add_basis_function)
    2483             :     {
    2484           0 :       if (optimal_value == 0.)
    2485             :         {
    2486           0 :           libMesh::out << "Encountered linearly dependent data in EIM enrichment, hence skip adding new basis function" << std::endl;
    2487           0 :           return true;
    2488             :         }
    2489             : 
    2490             :       // Scale local_pf so that its largest value is 1.0
    2491           0 :       scale_parametrized_function(local_pf, 1./optimal_value);
    2492             : 
    2493             :       // Add local_pf as the new basis function and store data
    2494             :       // associated with the interpolation point.
    2495           0 :       eim_eval.add_side_basis_function(local_pf);
    2496             :     }
    2497             : 
    2498           0 :   eim_eval.add_side_interpolation_data(optimal_point,
    2499             :                                        optimal_comp,
    2500             :                                        optimal_elem_id,
    2501             :                                        optimal_side_index,
    2502             :                                        optimal_subdomain_id,
    2503             :                                        optimal_boundary_id,
    2504             :                                        optimal_qp,
    2505             :                                        optimal_point_perturbs,
    2506             :                                        optimal_point_phi_i_qp);
    2507             : 
    2508             :   // In this case we did not encounter a linearly dependent basis function, so return false
    2509           0 :   return false;
    2510           0 : }
    2511             : 
    2512           0 : bool RBEIMConstruction::enrich_eim_approximation_on_nodes(const NodeDataMap & node_pf,
    2513             :                                                           bool add_basis_function,
    2514             :                                                           EimPointData * eim_point_data)
    2515             : {
    2516             :   // Make a copy of the input parametrized function, since we will modify this below
    2517             :   // to give us a new basis function.
    2518           0 :   NodeDataMap local_pf = node_pf;
    2519             : 
    2520           0 :   RBEIMEvaluation & eim_eval = get_rb_eim_evaluation();
    2521             : 
    2522             :   // If we have at least one basis function, then we need to use
    2523             :   // rb_eim_solve() to find the EIM interpolation error. Otherwise,
    2524             :   // just use solution as is.
    2525           0 :   if (!eim_point_data && (eim_eval.get_n_basis_functions() > 0))
    2526             :     {
    2527             :       // Get the right-hand side vector for the EIM approximation
    2528             :       // by sampling the parametrized function (stored in solution)
    2529             :       // at the interpolation points.
    2530           0 :       unsigned int RB_size = eim_eval.get_n_basis_functions();
    2531           0 :       DenseVector<Number> EIM_rhs(RB_size);
    2532           0 :       for (unsigned int i=0; i<RB_size; i++)
    2533             :         {
    2534           0 :           EIM_rhs(i) =
    2535           0 :             RBEIMEvaluation::get_parametrized_function_node_value(comm(),
    2536             :                                                                   local_pf,
    2537             :                                                                   eim_eval.get_interpolation_points_node_id(i),
    2538             :                                                                   eim_eval.get_interpolation_points_comp(i));
    2539             :         }
    2540             : 
    2541           0 :       eim_eval.set_parameters( get_parameters() );
    2542           0 :       DenseVector<Number> rb_eim_solution = eim_eval.rb_eim_solve(EIM_rhs);
    2543             : 
    2544             :       // Load the "EIM residual" into solution by subtracting
    2545             :       // the EIM approximation
    2546           0 :       eim_eval.node_decrement_vector(local_pf, rb_eim_solution);
    2547             :     }
    2548             : 
    2549             :   // Find the quadrature point at which local_pf (which now stores
    2550             :   // the "EIM residual") has maximum absolute value
    2551           0 :   Number optimal_value = 0.;
    2552           0 :   Point optimal_point;
    2553           0 :   unsigned int optimal_comp = 0;
    2554           0 :   dof_id_type optimal_node_id = DofObject::invalid_id;
    2555           0 :   boundary_id_type optimal_boundary_id = 0;
    2556             : 
    2557             :   // Initialize largest_abs_value to be negative so that it definitely gets updated.
    2558           0 :   Real largest_abs_value = -1.;
    2559             : 
    2560           0 :   for (const auto & [node_id, values] : local_pf)
    2561             :     {
    2562           0 :       for (unsigned int comp : index_range(values))
    2563             :         {
    2564           0 :           Number value = values[comp];
    2565           0 :           Real abs_value = std::abs(value);
    2566             : 
    2567           0 :           bool update_optimal_point = false;
    2568           0 :           if (!eim_point_data)
    2569           0 :             update_optimal_point = (abs_value > largest_abs_value);
    2570             :           else
    2571           0 :             update_optimal_point = (node_id == eim_point_data->node_id) &&
    2572           0 :                                    (comp == eim_point_data->comp_index);
    2573             : 
    2574           0 :           if (update_optimal_point)
    2575             :             {
    2576           0 :               largest_abs_value = abs_value;
    2577           0 :               optimal_value = value;
    2578           0 :               optimal_comp = comp;
    2579           0 :               optimal_node_id = node_id;
    2580             : 
    2581           0 :               optimal_point = libmesh_map_find(_local_node_locations, node_id);
    2582             : 
    2583           0 :               optimal_boundary_id = libmesh_map_find(_local_node_boundary_ids, node_id);
    2584             :             }
    2585             :         }
    2586             :     }
    2587             : 
    2588             :   // Find out which processor has the largest of the abs values
    2589             :   // and broadcast from that processor.
    2590             :   unsigned int proc_ID_index;
    2591           0 :   this->comm().maxloc(largest_abs_value, proc_ID_index);
    2592             : 
    2593           0 :   this->comm().broadcast(optimal_value, proc_ID_index);
    2594           0 :   this->comm().broadcast(optimal_point, proc_ID_index);
    2595           0 :   this->comm().broadcast(optimal_comp, proc_ID_index);
    2596           0 :   this->comm().broadcast(optimal_node_id, proc_ID_index);
    2597           0 :   this->comm().broadcast(optimal_boundary_id, proc_ID_index);
    2598             : 
    2599           0 :   libmesh_error_msg_if(optimal_node_id == DofObject::invalid_id, "Error: Invalid node ID");
    2600             : 
    2601           0 :   if (add_basis_function)
    2602             :     {
    2603           0 :       if (optimal_value == 0.)
    2604             :         {
    2605           0 :           libMesh::out << "Encountered linearly dependent data in EIM enrichment, hence skip adding new basis function" << std::endl;
    2606           0 :           return true;
    2607             :         }
    2608             : 
    2609             :       // Scale local_pf so that its largest value is 1.0
    2610           0 :       scale_node_parametrized_function(local_pf, 1./optimal_value);
    2611             : 
    2612             :       // Add local_pf as the new basis function and store data
    2613             :       // associated with the interpolation point.
    2614           0 :       eim_eval.add_node_basis_function(local_pf);
    2615             :     }
    2616             : 
    2617           0 :   eim_eval.add_node_interpolation_data(optimal_point,
    2618             :                                        optimal_comp,
    2619             :                                        optimal_node_id,
    2620             :                                        optimal_boundary_id);
    2621             : 
    2622             :   // In this case we did not encounter a linearly dependent basis function, so return false
    2623           0 :   return false;
    2624             : }
    2625             : 
    2626           0 : bool RBEIMConstruction::enrich_eim_approximation_on_interiors(const QpDataMap & interior_pf,
    2627             :                                                               bool add_basis_function,
    2628             :                                                               EimPointData * eim_point_data)
    2629             : {
    2630             :   // Make a copy of the input parametrized function, since we will modify this below
    2631             :   // to give us a new basis function.
    2632           0 :   QpDataMap local_pf = interior_pf;
    2633             : 
    2634           0 :   RBEIMEvaluation & eim_eval = get_rb_eim_evaluation();
    2635             : 
    2636             :   // If we have at least one basis function, then we need to use
    2637             :   // rb_eim_solve() to find the EIM interpolation error. Otherwise,
    2638             :   // just use solution as is.
    2639           0 :   if (!eim_point_data && (eim_eval.get_n_basis_functions() > 0))
    2640             :     {
    2641             :       // Get the right-hand side vector for the EIM approximation
    2642             :       // by sampling the parametrized function (stored in solution)
    2643             :       // at the interpolation points.
    2644           0 :       unsigned int RB_size = eim_eval.get_n_basis_functions();
    2645           0 :       DenseVector<Number> EIM_rhs(RB_size);
    2646           0 :       for (unsigned int i=0; i<RB_size; i++)
    2647             :         {
    2648           0 :           EIM_rhs(i) =
    2649           0 :             RBEIMEvaluation::get_parametrized_function_value(comm(),
    2650             :                                                             local_pf,
    2651             :                                                             eim_eval.get_interpolation_points_elem_id(i),
    2652             :                                                             eim_eval.get_interpolation_points_comp(i),
    2653             :                                                             eim_eval.get_interpolation_points_qp(i));
    2654             :         }
    2655             : 
    2656           0 :       eim_eval.set_parameters( get_parameters() );
    2657           0 :       DenseVector<Number> rb_eim_solution = eim_eval.rb_eim_solve(EIM_rhs);
    2658             : 
    2659             :       // Load the "EIM residual" into solution by subtracting
    2660             :       // the EIM approximation
    2661           0 :       eim_eval.decrement_vector(local_pf, rb_eim_solution);
    2662             :     }
    2663             : 
    2664             :   // Find the quadrature point at which local_pf (which now stores
    2665             :   // the "EIM residual") has maximum absolute value
    2666           0 :   Number optimal_value = 0.;
    2667           0 :   Point optimal_point;
    2668           0 :   unsigned int optimal_comp = 0;
    2669           0 :   dof_id_type optimal_elem_id = DofObject::invalid_id;
    2670           0 :   subdomain_id_type optimal_subdomain_id = 0;
    2671           0 :   unsigned int optimal_qp = 0;
    2672           0 :   std::vector<Point> optimal_point_perturbs;
    2673           0 :   std::vector<Real> optimal_point_phi_i_qp;
    2674           0 :   ElemType optimal_elem_type = INVALID_ELEM;
    2675           0 :   std::vector<Real> optimal_JxW_all_qp;
    2676           0 :   std::vector<std::vector<Real>> optimal_phi_i_all_qp;
    2677           0 :   Order optimal_qrule_order = INVALID_ORDER;
    2678           0 :   Point optimal_dxyzdxi_elem_center;
    2679           0 :   Point optimal_dxyzdeta_elem_center;
    2680             : 
    2681             :   // Initialize largest_abs_value to be negative so that it definitely gets updated.
    2682           0 :   Real largest_abs_value = -1.;
    2683             : 
    2684             :   // In order to compute phi_i_qp, we initialize a FEMContext
    2685           0 :   FEMContext con(*this);
    2686           0 :   for (auto dim : con.elem_dimensions())
    2687             :     {
    2688           0 :       auto fe = con.get_element_fe(/*var=*/0, dim);
    2689           0 :       fe->get_phi();
    2690           0 :       fe->get_JxW();
    2691           0 :       fe->get_dxyzdxi();
    2692           0 :       fe->get_dxyzdeta();
    2693             :     }
    2694             : 
    2695           0 :   for (const auto & [elem_id, comp_and_qp] : local_pf)
    2696             :     {
    2697             :       // Also initialize phi in order to compute phi_i_qp
    2698           0 :       const Elem & elem_ref = get_mesh().elem_ref(elem_id);
    2699           0 :       con.pre_fe_reinit(*this, &elem_ref);
    2700             : 
    2701           0 :       auto elem_fe = con.get_element_fe(/*var=*/0, elem_ref.dim());
    2702           0 :       const std::vector<std::vector<Real>> & phi = elem_fe->get_phi();
    2703           0 :       const auto & JxW = elem_fe->get_JxW();
    2704           0 :       const auto & dxyzdxi = elem_fe->get_dxyzdxi();
    2705           0 :       const auto & dxyzdeta = elem_fe->get_dxyzdeta();
    2706             : 
    2707           0 :       elem_fe->reinit(&elem_ref);
    2708             : 
    2709           0 :       for (const auto & comp : index_range(comp_and_qp))
    2710             :         {
    2711           0 :           const std::vector<Number> & qp_values = comp_and_qp[comp];
    2712             : 
    2713           0 :           for (auto qp : index_range(qp_values))
    2714             :             {
    2715           0 :               Number value = qp_values[qp];
    2716           0 :               Real abs_value = std::abs(value);
    2717             : 
    2718           0 :               if (get_rb_eim_evaluation().scale_components_in_enrichment().count(comp))
    2719           0 :                 abs_value *= _component_scaling_in_training_set[comp];
    2720             : 
    2721           0 :               bool update_optimal_point = false;
    2722           0 :               if (!eim_point_data)
    2723           0 :                 update_optimal_point = (abs_value > largest_abs_value);
    2724             :               else
    2725           0 :                 update_optimal_point = (elem_id == eim_point_data->elem_id) &&
    2726           0 :                                        (comp == eim_point_data->comp_index) &&
    2727           0 :                                        (qp == eim_point_data->qp_index);
    2728             : 
    2729           0 :               if (update_optimal_point)
    2730             :                 {
    2731           0 :                   largest_abs_value = abs_value;
    2732           0 :                   optimal_value = value;
    2733           0 :                   optimal_comp = comp;
    2734           0 :                   optimal_elem_id = elem_id;
    2735           0 :                   optimal_qp = qp;
    2736           0 :                   optimal_elem_type = elem_ref.type();
    2737             : 
    2738           0 :                   optimal_point_phi_i_qp.resize(phi.size());
    2739           0 :                   for (auto i : index_range(phi))
    2740           0 :                     optimal_point_phi_i_qp[i] = phi[i][qp];
    2741             : 
    2742             :                   const auto & point_list =
    2743           0 :                     libmesh_map_find(_local_quad_point_locations, elem_id);
    2744             : 
    2745           0 :                   libmesh_error_msg_if(qp >= point_list.size(), "Error: Invalid qp");
    2746             : 
    2747           0 :                   optimal_point = point_list[qp];
    2748             : 
    2749           0 :                   optimal_subdomain_id = libmesh_map_find(_local_quad_point_subdomain_ids, elem_id);
    2750             : 
    2751           0 :                   if (get_rb_eim_evaluation().get_parametrized_function().requires_xyz_perturbations)
    2752             :                     {
    2753             :                       const auto & perturb_list =
    2754           0 :                         libmesh_map_find(_local_quad_point_locations_perturbations, elem_id);
    2755             : 
    2756           0 :                       libmesh_error_msg_if(qp >= perturb_list.size(), "Error: Invalid qp");
    2757             : 
    2758           0 :                       optimal_point_perturbs = perturb_list[qp];
    2759             :                     }
    2760             : 
    2761           0 :                   if (get_rb_eim_evaluation().get_parametrized_function().requires_all_elem_qp_data)
    2762             :                     {
    2763           0 :                       optimal_JxW_all_qp = JxW;
    2764           0 :                       optimal_phi_i_all_qp = phi;
    2765             :                     }
    2766             : 
    2767           0 :                   if (get_rb_eim_evaluation().get_parametrized_function().requires_all_elem_center_data)
    2768             :                     {
    2769           0 :                       optimal_qrule_order = con.get_element_qrule().get_order();
    2770             :                       // Get data derivatives at vertex average
    2771           0 :                       std::vector<Point> nodes = { elem_ref.reference_elem()->vertex_average() };
    2772           0 :                       elem_fe->reinit (&elem_ref, &nodes);
    2773             : 
    2774           0 :                       Point dxyzdxi_pt, dxyzdeta_pt;
    2775           0 :                       if (con.get_elem_dim()>0)
    2776           0 :                         dxyzdxi_pt = dxyzdxi[0];
    2777           0 :                       if (con.get_elem_dim()>1)
    2778           0 :                         dxyzdeta_pt = dxyzdeta[0];
    2779             : 
    2780           0 :                       optimal_dxyzdxi_elem_center = dxyzdxi_pt;
    2781           0 :                       optimal_dxyzdeta_elem_center = dxyzdeta_pt;
    2782             : 
    2783           0 :                       elem_fe->reinit(&elem_ref);
    2784             :                     }
    2785             :                 }
    2786             :             }
    2787             :         }
    2788             :     }
    2789             : 
    2790             :   // Find out which processor has the largest of the abs values
    2791             :   // and broadcast from that processor.
    2792             :   unsigned int proc_ID_index;
    2793           0 :   this->comm().maxloc(largest_abs_value, proc_ID_index);
    2794             : 
    2795           0 :   this->comm().broadcast(optimal_value, proc_ID_index);
    2796           0 :   this->comm().broadcast(optimal_point, proc_ID_index);
    2797           0 :   this->comm().broadcast(optimal_comp, proc_ID_index);
    2798           0 :   this->comm().broadcast(optimal_elem_id, proc_ID_index);
    2799           0 :   this->comm().broadcast(optimal_subdomain_id, proc_ID_index);
    2800           0 :   this->comm().broadcast(optimal_qp, proc_ID_index);
    2801           0 :   this->comm().broadcast(optimal_point_perturbs, proc_ID_index);
    2802           0 :   this->comm().broadcast(optimal_point_phi_i_qp, proc_ID_index);
    2803           0 :   this->comm().broadcast(optimal_JxW_all_qp, proc_ID_index);
    2804           0 :   this->comm().broadcast(optimal_phi_i_all_qp, proc_ID_index);
    2805           0 :   this->comm().broadcast(optimal_dxyzdxi_elem_center, proc_ID_index);
    2806           0 :   this->comm().broadcast(optimal_dxyzdeta_elem_center, proc_ID_index);
    2807             : 
    2808             :   // Cast optimal_elem_type to an int in order to broadcast it
    2809             :   {
    2810           0 :     int optimal_elem_type_int = static_cast<int>(optimal_elem_type);
    2811           0 :     this->comm().broadcast(optimal_elem_type_int, proc_ID_index);
    2812           0 :     optimal_elem_type = static_cast<ElemType>(optimal_elem_type_int);
    2813             :   }
    2814             : 
    2815             :   // Cast optimal_qrule_order to an int in order to broadcast it
    2816             :   {
    2817           0 :     int optimal_qrule_order_int = static_cast<int>(optimal_qrule_order);
    2818           0 :     this->comm().broadcast(optimal_qrule_order_int, proc_ID_index);
    2819           0 :     optimal_qrule_order = static_cast<Order>(optimal_qrule_order_int);
    2820             :   }
    2821             : 
    2822           0 :   libmesh_error_msg_if(optimal_elem_id == DofObject::invalid_id, "Error: Invalid element ID");
    2823             : 
    2824           0 :   if (add_basis_function)
    2825             :     {
    2826           0 :       if (optimal_value == 0.)
    2827             :         {
    2828           0 :           libMesh::out << "Encountered linearly dependent data in EIM enrichment, hence skip adding new basis function" << std::endl;
    2829           0 :           return true;
    2830             :         }
    2831             : 
    2832             :       // Scale local_pf so that its largest value is 1.0
    2833           0 :       scale_parametrized_function(local_pf, 1./optimal_value);
    2834             : 
    2835             :       // Add local_pf as the new basis function and store data
    2836             :       // associated with the interpolation point.
    2837           0 :       eim_eval.add_basis_function(local_pf);
    2838             :     }
    2839             : 
    2840           0 :   eim_eval.add_interpolation_data(optimal_point,
    2841             :                                   optimal_comp,
    2842             :                                   optimal_elem_id,
    2843             :                                   optimal_subdomain_id,
    2844             :                                   optimal_qp,
    2845             :                                   optimal_point_perturbs,
    2846             :                                   optimal_point_phi_i_qp,
    2847             :                                   optimal_elem_type,
    2848             :                                   optimal_JxW_all_qp,
    2849             :                                   optimal_phi_i_all_qp,
    2850             :                                   optimal_qrule_order,
    2851             :                                   optimal_dxyzdxi_elem_center,
    2852             :                                   optimal_dxyzdeta_elem_center);
    2853             : 
    2854             :   // In this case we did not encounter a linearly dependent basis function, so return false
    2855           0 :   return false;
    2856           0 : }
    2857             : 
    2858           0 : void RBEIMConstruction::update_eim_matrices(bool set_eim_error_indicator)
    2859             : {
    2860           0 :   LOG_SCOPE("update_eim_matrices()", "RBEIMConstruction");
    2861             : 
    2862           0 :   RBEIMEvaluation & eim_eval = get_rb_eim_evaluation();
    2863           0 :   unsigned int RB_size = eim_eval.get_n_basis_functions();
    2864             : 
    2865           0 :   libmesh_assert_msg(RB_size >= 1, "Must have at least 1 basis function.");
    2866             : 
    2867           0 :   if (set_eim_error_indicator)
    2868             :     {
    2869             :       // Here we have RB_size EIM basis functions, and RB_size+1 interpolation points,
    2870             :       // since we should have added one extra interpolation point for the EIM error
    2871             :       // indicator. As a result, we use RB_size as the index to access the (RB_size+1)^th
    2872             :       // interpolation point in the calls to eim_eval.get_interpolation_points_*.
    2873           0 :       DenseVector<Number> extra_point_row(RB_size);
    2874             : 
    2875           0 :       if (eim_eval.get_parametrized_function().on_mesh_sides())
    2876             :         {
    2877             :           // update the EIM interpolation matrix
    2878           0 :           for (unsigned int j=0; j<RB_size; j++)
    2879             :             {
    2880             :               // Evaluate the basis functions at the new interpolation point in order
    2881             :               // to update the interpolation matrix
    2882             :               Number value =
    2883           0 :                 eim_eval.get_eim_basis_function_side_value(j,
    2884             :                                                            eim_eval.get_interpolation_points_elem_id(RB_size),
    2885             :                                                            eim_eval.get_interpolation_points_side_index(RB_size),
    2886             :                                                            eim_eval.get_interpolation_points_comp(RB_size),
    2887             :                                                            eim_eval.get_interpolation_points_qp(RB_size));
    2888           0 :               extra_point_row(j) = value;
    2889             :             }
    2890             :         }
    2891           0 :       else if (eim_eval.get_parametrized_function().on_mesh_nodes())
    2892             :         {
    2893             :           // update the EIM interpolation matrix
    2894           0 :           for (unsigned int j=0; j<RB_size; j++)
    2895             :             {
    2896             :               // Evaluate the basis functions at the new interpolation point in order
    2897             :               // to update the interpolation matrix
    2898             :               Number value =
    2899           0 :                 eim_eval.get_eim_basis_function_node_value(j,
    2900             :                                                            eim_eval.get_interpolation_points_node_id(RB_size),
    2901             :                                                            eim_eval.get_interpolation_points_comp(RB_size));
    2902           0 :               extra_point_row(j) = value;
    2903             :             }
    2904             :         }
    2905             :       else
    2906             :         {
    2907             :           // update the EIM interpolation matrix
    2908           0 :           for (unsigned int j=0; j<RB_size; j++)
    2909             :             {
    2910             :               // Evaluate the basis functions at the new interpolation point in order
    2911             :               // to update the interpolation matrix
    2912             :               Number value =
    2913           0 :                 eim_eval.get_eim_basis_function_value(j,
    2914             :                                                       eim_eval.get_interpolation_points_elem_id(RB_size),
    2915             :                                                       eim_eval.get_interpolation_points_comp(RB_size),
    2916             :                                                       eim_eval.get_interpolation_points_qp(RB_size));
    2917           0 :               extra_point_row(j) = value;
    2918             :             }
    2919             :         }
    2920             : 
    2921           0 :       eim_eval.set_error_indicator_interpolation_row(extra_point_row);
    2922           0 :       return;
    2923             :     }
    2924             : 
    2925           0 :   if (eim_eval.get_parametrized_function().on_mesh_sides())
    2926             :     {
    2927             :       // update the matrix that is used to evaluate L2 projections
    2928             :       // into the EIM approximation space
    2929           0 :       for (unsigned int i=(RB_size-1); i<RB_size; i++)
    2930             :         {
    2931           0 :           for (unsigned int j=0; j<RB_size; j++)
    2932             :             {
    2933           0 :               Number value = side_inner_product(eim_eval.get_side_basis_function(j),
    2934           0 :                                                 eim_eval.get_side_basis_function(i),
    2935             :                                                 /*apply_comp_scaling*/ false);
    2936             : 
    2937           0 :               _eim_projection_matrix(i,j) = value;
    2938           0 :               if (i!=j)
    2939             :                 {
    2940             :                   // The inner product matrix is assumed to be hermitian
    2941           0 :                   _eim_projection_matrix(j,i) = libmesh_conj(value);
    2942             :                 }
    2943             :             }
    2944             :         }
    2945             : 
    2946             :       // update the EIM interpolation matrix
    2947           0 :       for (unsigned int j=0; j<RB_size; j++)
    2948             :         {
    2949             :           // Evaluate the basis functions at the new interpolation point in order
    2950             :           // to update the interpolation matrix
    2951             :           Number value =
    2952           0 :             eim_eval.get_eim_basis_function_side_value(j,
    2953             :                                                        eim_eval.get_interpolation_points_elem_id(RB_size-1),
    2954             :                                                        eim_eval.get_interpolation_points_side_index(RB_size-1),
    2955             :                                                        eim_eval.get_interpolation_points_comp(RB_size-1),
    2956             :                                                        eim_eval.get_interpolation_points_qp(RB_size-1));
    2957           0 :           eim_eval.set_interpolation_matrix_entry(RB_size-1, j, value);
    2958             :         }
    2959             :     }
    2960           0 :   else if (eim_eval.get_parametrized_function().on_mesh_nodes())
    2961             :     {
    2962             :       // update the matrix that is used to evaluate L2 projections
    2963             :       // into the EIM approximation space
    2964           0 :       for (unsigned int i=(RB_size-1); i<RB_size; i++)
    2965             :         {
    2966           0 :           for (unsigned int j=0; j<RB_size; j++)
    2967             :             {
    2968           0 :               Number value = node_inner_product(eim_eval.get_node_basis_function(j),
    2969           0 :                                                 eim_eval.get_node_basis_function(i),
    2970             :                                                 /*apply_comp_scaling*/ false);
    2971             : 
    2972           0 :               _eim_projection_matrix(i,j) = value;
    2973           0 :               if (i!=j)
    2974             :                 {
    2975             :                   // The inner product matrix is assumed to be hermitian
    2976           0 :                   _eim_projection_matrix(j,i) = libmesh_conj(value);
    2977             :                 }
    2978             :             }
    2979             :         }
    2980             : 
    2981             :       // update the EIM interpolation matrix
    2982           0 :       for (unsigned int j=0; j<RB_size; j++)
    2983             :         {
    2984             :           // Evaluate the basis functions at the new interpolation point in order
    2985             :           // to update the interpolation matrix
    2986             :           Number value =
    2987           0 :             eim_eval.get_eim_basis_function_node_value(j,
    2988             :                                                        eim_eval.get_interpolation_points_node_id(RB_size-1),
    2989             :                                                        eim_eval.get_interpolation_points_comp(RB_size-1));
    2990           0 :           eim_eval.set_interpolation_matrix_entry(RB_size-1, j, value);
    2991             :         }
    2992             :     }
    2993             :   else
    2994             :     {
    2995             :       // update the matrix that is used to evaluate L2 projections
    2996             :       // into the EIM approximation space
    2997           0 :       for (unsigned int i=(RB_size-1); i<RB_size; i++)
    2998             :         {
    2999           0 :           for (unsigned int j=0; j<RB_size; j++)
    3000             :             {
    3001           0 :               Number value = inner_product(eim_eval.get_basis_function(j),
    3002           0 :                                            eim_eval.get_basis_function(i),
    3003             :                                            /*apply_comp_scaling*/ false);
    3004             : 
    3005           0 :               _eim_projection_matrix(i,j) = value;
    3006           0 :               if (i!=j)
    3007             :                 {
    3008             :                   // The inner product matrix is assumed to be hermitian
    3009           0 :                   _eim_projection_matrix(j,i) = libmesh_conj(value);
    3010             :                 }
    3011             :             }
    3012             :         }
    3013             : 
    3014             :       // update the EIM interpolation matrix
    3015           0 :       for (unsigned int j=0; j<RB_size; j++)
    3016             :         {
    3017             :           // Evaluate the basis functions at the new interpolation point in order
    3018             :           // to update the interpolation matrix
    3019             :           Number value =
    3020           0 :             eim_eval.get_eim_basis_function_value(j,
    3021             :                                                   eim_eval.get_interpolation_points_elem_id(RB_size-1),
    3022             :                                                   eim_eval.get_interpolation_points_comp(RB_size-1),
    3023             :                                                   eim_eval.get_interpolation_points_qp(RB_size-1));
    3024           0 :           eim_eval.set_interpolation_matrix_entry(RB_size-1, j, value);
    3025             :         }
    3026             :     }
    3027             : }
    3028             : 
    3029           0 : void RBEIMConstruction::scale_node_parametrized_function(NodeDataMap & local_pf,
    3030             :                                                          Number scaling_factor)
    3031             : {
    3032           0 :   for (auto & pr : local_pf)
    3033             :     {
    3034           0 :       auto & values = pr.second;
    3035           0 :       for ( auto & value : values)
    3036           0 :         value *= scaling_factor;
    3037             :     }
    3038           0 : }
    3039             : 
    3040           0 : unsigned int RBEIMConstruction::get_random_int_0_to_n(unsigned int n)
    3041             : {
    3042             :   // std::random_device seed;
    3043             :   // std::mt19937 gen{seed()};
    3044             :   // We do not use a random seed here, since we generally prefer our results
    3045             :   // to reproducible, rather than fully random. If desired we could provide an
    3046             :   // option to use the random seed approach (commented out above).
    3047           0 :   std::default_random_engine gen;
    3048           0 :   std::uniform_int_distribution<> dist{0, static_cast<int>(n)};
    3049           0 :   return dist(gen);
    3050             : }
    3051             : 
    3052           0 : EimPointData RBEIMConstruction::get_random_point(const QpDataMap & v)
    3053             : {
    3054             :   EimPointData eim_point_data;
    3055             : 
    3056             :   // If we have more than one process, then we need to do a parallel union
    3057             :   // of v to make sure that we have data from all processors. Our approach
    3058             :   // here is to set v_ptr to either v or global_v, depending on whether we
    3059             :   // are in parallel or serial. The purpose of this approach is to avoid
    3060             :   // making a copy of v in the case that this is a serial job.
    3061           0 :   QpDataMap const * v_ptr = nullptr;
    3062           0 :   QpDataMap global_v;
    3063           0 :   if (comm().size() > 1)
    3064             :   {
    3065           0 :     global_v = v;
    3066             : 
    3067             :     // We only use global_v on proc 0, so we set the second argument of
    3068             :     // set_union() to zero here to indicate that we only need the result
    3069             :     // on proc 0.
    3070           0 :     comm().set_union(global_v, 0);
    3071           0 :     v_ptr = &global_v;
    3072             :   }
    3073             :   else
    3074             :   {
    3075           0 :     v_ptr = &v;
    3076             :   }
    3077             : 
    3078           0 :   bool error_finding_new_element = false;
    3079           0 :   if (comm().rank() == 0)
    3080             :     {
    3081           0 :       const VectorizedEvalInput & vec_eval_input = get_rb_eim_evaluation().get_vec_eval_input();
    3082             : 
    3083             :       {
    3084           0 :         std::set<dof_id_type> previous_elem_ids(vec_eval_input.elem_ids.begin(), vec_eval_input.elem_ids.end());
    3085             : 
    3086             :         // We ensure that we select a point that has not been selected previously
    3087             :         // by setting up new_elem_ids to contain only elements that are not in
    3088             :         // previous_elem_ids, and then selecting the elem_id at random from new_elem_ids.
    3089             :         // We give an error if there are no elements in new_elem_ids. This is potentially
    3090             :         // an overzealous assertion since we could pick an element that has already
    3091             :         // been selected as long as we pick a (comp_index, qp_index) that has not already
    3092             :         // been selected for that element.
    3093             :         //
    3094             :         // However, in general we do not expect all elements to be selected in the EIM
    3095             :         // training, so it is reasonable to use the simple assertion below. Moreover, by
    3096             :         // ensuring that we choose a new element we should typically ensure that the
    3097             :         // randomly selected point has some separation from the previous EIM points, which
    3098             :         // is typically desirable if we want EIM evaluations that are independent from
    3099             :         // the EIM points (e.g. for EIM error indicator purposes).
    3100           0 :         std::set<dof_id_type> new_elem_ids;
    3101           0 :         for (const auto & v_pair : *v_ptr)
    3102           0 :           if (previous_elem_ids.count(v_pair.first) == 0)
    3103           0 :             new_elem_ids.insert(v_pair.first);
    3104             : 
    3105             :         // If new_elem_ids is empty then we set error_finding_new_element to true.
    3106             :         // We then broadcast the value of error_finding_new_element to all processors
    3107             :         // below in order to ensure that all processors agree on whether or not
    3108             :         // there was an error.
    3109           0 :         error_finding_new_element = (new_elem_ids.empty());
    3110             : 
    3111           0 :         if (!error_finding_new_element)
    3112             :           {
    3113           0 :             unsigned int random_elem_idx = get_random_int_0_to_n(new_elem_ids.size()-1);
    3114             : 
    3115           0 :             auto item = new_elem_ids.begin();
    3116           0 :             std::advance(item, random_elem_idx);
    3117           0 :             eim_point_data.elem_id = *item;
    3118             :           }
    3119             :       }
    3120             : 
    3121           0 :       if (!error_finding_new_element)
    3122             :         {
    3123             :           {
    3124           0 :             const auto & vars_and_qps = libmesh_map_find(*v_ptr,eim_point_data.elem_id);
    3125           0 :             eim_point_data.comp_index = get_random_int_0_to_n(vars_and_qps.size()-1);
    3126             :           }
    3127             : 
    3128             :           {
    3129           0 :             const auto & qps = libmesh_map_find(*v_ptr,eim_point_data.elem_id)[eim_point_data.comp_index];
    3130           0 :             eim_point_data.qp_index = get_random_int_0_to_n(qps.size()-1);
    3131             :           }
    3132             :         }
    3133             :     }
    3134             : 
    3135           0 :   comm().broadcast(error_finding_new_element);
    3136           0 :   libmesh_error_msg_if(error_finding_new_element, "Could not find new element in get_random_point()");
    3137             : 
    3138             :   // Broadcast the values computed above from rank 0
    3139           0 :   comm().broadcast(eim_point_data.elem_id);
    3140           0 :   comm().broadcast(eim_point_data.comp_index);
    3141           0 :   comm().broadcast(eim_point_data.qp_index);
    3142             : 
    3143           0 :   return eim_point_data;
    3144             : }
    3145             : 
    3146           0 : EimPointData RBEIMConstruction::get_random_point(const SideQpDataMap & v)
    3147             : {
    3148             :   EimPointData eim_point_data;
    3149             : 
    3150             :   // If we have more than one process, then we need to do a parallel union
    3151             :   // of v to make sure that we have data from all processors. Our approach
    3152             :   // here is to set v_ptr to either v or global_v, depending on whether we
    3153             :   // are in parallel or serial. The purpose of this approach is to avoid
    3154             :   // making a copy of v in the case that this is a serial job.
    3155           0 :   SideQpDataMap const * v_ptr = nullptr;
    3156           0 :   SideQpDataMap global_v;
    3157           0 :   if (comm().size() > 1)
    3158             :   {
    3159           0 :     global_v = v;
    3160             : 
    3161             :     // We only use global_v on proc 0, so we set the second argument of
    3162             :     // set_union() to zero here to indicate that we only need the result
    3163             :     // on proc 0.
    3164           0 :     comm().set_union(global_v, 0);
    3165           0 :     v_ptr = &global_v;
    3166             :   }
    3167             :   else
    3168             :   {
    3169           0 :     v_ptr = &v;
    3170             :   }
    3171             : 
    3172           0 :   bool error_finding_new_element_and_side = false;
    3173           0 :   if (comm().rank() == 0)
    3174             :     {
    3175           0 :       const VectorizedEvalInput & vec_eval_input = get_rb_eim_evaluation().get_vec_eval_input();
    3176             : 
    3177           0 :       std::pair<dof_id_type,unsigned int> elem_and_side;
    3178             :       {
    3179           0 :         std::set<std::pair<dof_id_type,unsigned int>> previous_elem_and_side_ids;
    3180           0 :         for (const auto idx : index_range(vec_eval_input.elem_ids))
    3181             :           {
    3182           0 :             previous_elem_and_side_ids.insert(
    3183           0 :               std::make_pair(vec_eval_input.elem_ids[idx],
    3184           0 :                              vec_eval_input.side_indices[idx]));
    3185             :           }
    3186             : 
    3187             :         // See discussion above in the QpDataMap case for the justification
    3188             :         // of how we set up new_elem_and_side_ids below.
    3189           0 :         std::set<std::pair<dof_id_type,unsigned int>> new_elem_and_side_ids;
    3190           0 :         for (const auto & v_pair : *v_ptr)
    3191           0 :           if (previous_elem_and_side_ids.count(v_pair.first) == 0)
    3192           0 :             new_elem_and_side_ids.insert(v_pair.first);
    3193             : 
    3194             :         // If new_elem_and_side_ids is empty then we set error_finding_new_element_and_side
    3195             :         // to true. We then broadcast the value of error_finding_new_element_and_side to all
    3196             :         // processors below in order to ensure that all processors agree on whether
    3197             :         // or not there was an error.
    3198           0 :         error_finding_new_element_and_side = (new_elem_and_side_ids.empty());
    3199             : 
    3200           0 :         if (!error_finding_new_element_and_side)
    3201             :           {
    3202           0 :             unsigned int random_elem_and_side_idx = get_random_int_0_to_n(new_elem_and_side_ids.size()-1);
    3203             : 
    3204           0 :             auto item = new_elem_and_side_ids.begin();
    3205           0 :             std::advance(item, random_elem_and_side_idx);
    3206           0 :             elem_and_side = *item;
    3207           0 :             eim_point_data.elem_id = elem_and_side.first;
    3208           0 :             eim_point_data.side_index = elem_and_side.second;
    3209             :           }
    3210             :       }
    3211             : 
    3212           0 :       if (!error_finding_new_element_and_side)
    3213             :         {
    3214             :           {
    3215           0 :             const auto & vars_and_qps = libmesh_map_find(*v_ptr,elem_and_side);
    3216           0 :             eim_point_data.comp_index = get_random_int_0_to_n(vars_and_qps.size()-1);
    3217             :           }
    3218             : 
    3219             :           {
    3220           0 :             const auto & qps = libmesh_map_find(*v_ptr,elem_and_side)[eim_point_data.comp_index];
    3221           0 :             eim_point_data.qp_index = get_random_int_0_to_n(qps.size()-1);
    3222             :           }
    3223             :         }
    3224             :     }
    3225             : 
    3226           0 :   comm().broadcast(error_finding_new_element_and_side);
    3227           0 :   libmesh_error_msg_if(error_finding_new_element_and_side, "Could not find new (element,side) in get_random_point()");
    3228             : 
    3229             :   // Broadcast the values computed above from rank 0
    3230           0 :   comm().broadcast(eim_point_data.elem_id);
    3231           0 :   comm().broadcast(eim_point_data.side_index);
    3232           0 :   comm().broadcast(eim_point_data.comp_index);
    3233           0 :   comm().broadcast(eim_point_data.qp_index);
    3234             : 
    3235           0 :   return eim_point_data;
    3236             : }
    3237             : 
    3238           0 : EimPointData RBEIMConstruction::get_random_point(const NodeDataMap & v)
    3239             : {
    3240             :   EimPointData eim_point_data;
    3241             : 
    3242             :   // If we have more than one process, then we need to do a parallel union
    3243             :   // of v to make sure that we have data from all processors. Our approach
    3244             :   // here is to set v_ptr to either v or global_v, depending on whether we
    3245             :   // are in parallel or serial. The purpose of this approach is to avoid
    3246             :   // making a copy of v in the case that this is a serial job.
    3247           0 :   NodeDataMap const * v_ptr = nullptr;
    3248           0 :   NodeDataMap global_v;
    3249           0 :   if (comm().size() > 1)
    3250             :   {
    3251           0 :     global_v = v;
    3252             : 
    3253             :     // We only use global_v on proc 0, so we set the second argument of
    3254             :     // set_union() to zero here to indicate that we only need the result
    3255             :     // on proc 0.
    3256           0 :     comm().set_union(global_v, 0);
    3257           0 :     v_ptr = &global_v;
    3258             :   }
    3259             :   else
    3260             :   {
    3261           0 :     v_ptr = &v;
    3262             :   }
    3263             : 
    3264           0 :   bool error_finding_new_node = false;
    3265           0 :   if (comm().rank() == 0)
    3266             :     {
    3267           0 :       const VectorizedEvalInput & vec_eval_input = get_rb_eim_evaluation().get_vec_eval_input();
    3268             : 
    3269             :       {
    3270           0 :         std::set<dof_id_type> previous_node_ids(vec_eval_input.node_ids.begin(), vec_eval_input.node_ids.end());
    3271             : 
    3272             :         // See discussion above in the QpDataMap case for the justification
    3273             :         // of how we set up new_node_ids below.
    3274           0 :         std::set<dof_id_type> new_node_ids;
    3275           0 :         for (const auto & v_pair : *v_ptr)
    3276           0 :           if (previous_node_ids.count(v_pair.first) == 0)
    3277           0 :             new_node_ids.insert(v_pair.first);
    3278             : 
    3279             :         // If new_node_ids is empty then we set error_finding_new_node
    3280             :         // to true. We then broadcast the value of error_finding_new_node to all
    3281             :         // processors below in order to ensure that all processors agree on whether
    3282             :         // or not there was an error.
    3283           0 :         error_finding_new_node = (new_node_ids.empty());
    3284             : 
    3285           0 :         if (!error_finding_new_node)
    3286             :           {
    3287           0 :             unsigned int random_node_idx = get_random_int_0_to_n(new_node_ids.size()-1);
    3288             : 
    3289           0 :             auto item = new_node_ids.begin();
    3290           0 :             std::advance(item, random_node_idx);
    3291           0 :             eim_point_data.node_id = *item;
    3292             :           }
    3293             :       }
    3294             : 
    3295           0 :       if (!error_finding_new_node)
    3296             :         {
    3297           0 :           const auto & vars = libmesh_map_find(*v_ptr,eim_point_data.node_id);
    3298           0 :           eim_point_data.comp_index = get_random_int_0_to_n(vars.size()-1);
    3299             :         }
    3300             :     }
    3301             : 
    3302           0 :   comm().broadcast(error_finding_new_node);
    3303           0 :   libmesh_error_msg_if(error_finding_new_node, "Could not find new node in get_random_point()");
    3304             : 
    3305             :   // Broadcast the values computed above from rank 0
    3306           0 :   comm().broadcast(eim_point_data.node_id);
    3307           0 :   comm().broadcast(eim_point_data.comp_index);
    3308             : 
    3309           0 :   return eim_point_data;
    3310             : }
    3311             : 
    3312           0 : EimPointData RBEIMConstruction::get_random_point_from_training_sample()
    3313             : {
    3314           0 :   RBEIMEvaluation & eim_eval = get_rb_eim_evaluation();
    3315             : 
    3316           0 :   if (eim_eval.get_parametrized_function().on_mesh_sides())
    3317           0 :     return get_random_point(_local_side_parametrized_functions_for_training[0]);
    3318           0 :   else if (eim_eval.get_parametrized_function().on_mesh_nodes())
    3319           0 :     return get_random_point(_local_node_parametrized_functions_for_training[0]);
    3320             :   else
    3321           0 :     return get_random_point(_local_parametrized_functions_for_training[0]);
    3322             : }
    3323             : 
    3324             : } // namespace libMesh

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