Line data    Source code

       1             : // The libMesh Finite Element Library.
       2             : // Copyright (C) 2002-2026 Benjamin S. Kirk, John W. Peterson, Roy H. Stogner
       3             : 
       4             : // This library is free software; you can redistribute it and/or
       5             : // modify it under the terms of the GNU Lesser General Public
       6             : // License as published by the Free Software Foundation; either
       7             : // version 2.1 of the License, or (at your option) any later version.
       8             : 
       9             : // This library is distributed in the hope that it will be useful,
      10             : // but WITHOUT ANY WARRANTY; without even the implied warranty of
      11             : // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      12             : // Lesser General Public License for more details.
      13             : 
      14             : // You should have received a copy of the GNU Lesser General Public
      15             : // License along with this library; if not, write to the Free Software
      16             : // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
      17             : 
      18             : #ifndef LIBMESH_STATIC_CONDENSATION_DOF_MAP_H
      19             : #define LIBMESH_STATIC_CONDENSATION_DOF_MAP_H
      20             : 
      21             : #include "libmesh/libmesh_config.h"
      22             : 
      23             : #include "libmesh/id_types.h"
      24             : #include "libmesh/libmesh_common.h"
      25             : #include "libmesh/reduced_dof_map.h"
      26             : 
      27             : #include <unordered_map>
      28             : #include <unordered_set>
      29             : 
      30             : namespace libMesh
      31             : {
      32             : class MeshBase;
      33             : class System;
      34             : class DofMap;
      35             : class Elem;
      36             : 
      37             : /**
      38             :  * A class holding degree of freedom information pertinent to static condensation.
      39             :  * Static condensation is a process for reducing the number of unknowns in a
      40             :  * linear(ized) system. It is often used in conjunction with a hybridized discontinuous Galerkin
      41             :  * (HDG) method to reduce the number of unknowns in the linear system to something more on the order
      42             :  * of a continuous Galerkin (CG) method as opposed to a discontinuous Galerkin method. In the HDG
      43             :  * example, degrees of freedom on the element interiors are condensed out and only the degrees of
      44             :  * freedom on element faces are retained in the condensed system. Static condensation is not only
      45             :  * applicable to HDG methods, however. One could also use static condensation with a high order CG
      46             :  * method, again removing internal degrees of freedom and leaving those on element boundaries.
      47             :  *
      48             :  * Users may query this class for condensed space degree of freedom information associated with
      49             :  * elements. Queries with nodes are not supported. This class also holds information for mapping
      50             :  * degree of freedom indices in the global, uncondensed space to local element degree of freedom
      51             :  * numbers. This information is essential in order to build the element Schur complement matrices
      52             :  * that are used to map global system vector and matrix data to the condensed system vector and
      53             :  * matrix data
      54             :  */
      55          90 : class StaticCondensationDofMap : public ReducedDofMap
      56             : {
      57             : public:
      58             :   StaticCondensationDofMap(MeshBase & mesh, System & system, const DofMap & dof_map);
      59             :   virtual ~StaticCondensationDofMap();
      60             : 
      61             :   /**
      62             :    * Build the reduced space and the element global to local index maps
      63             :    */
      64             :   virtual void reinit() override;
      65             : 
      66             :   /**
      67             :    * Add \p vars to the list of variables not to condense. This can be useful when some variable's
      68             :    * equation is discretized with a DG method or if including the variable in the condensed block
      69             :    * diagonal would result in it being singular
      70             :    */
      71             :   void dont_condense_vars(const std::unordered_set<unsigned int> & vars);
      72             : 
      73             :   /**
      74             :    * @returns our list of variables for whom we do not condense out any dofs
      75             :    */
      76             :   const std::unordered_set<unsigned int> & uncondensed_vars() const { return _uncondensed_vars; }
      77             : 
      78             :   virtual void clear() override;
      79             : 
      80             :   /**
      81             :    * Degrees of freedom on element boundaries and degrees of freedom of uncondensed variables are
      82             :    * retained
      83             :    */
      84             :   virtual bool retain_field_dof(const Elem & elem,
      85             :                                 unsigned int node_num,
      86             :                                 unsigned int var_num,
      87             :                                 dof_id_type field_dof) const override;
      88             : 
      89             : protected:
      90             :   virtual void retained_dof_added(const Elem & elem, dof_id_type full_dof) override;
      91             : 
      92             :   virtual void unretained_dof_found(const Elem & elem, dof_id_type full_dof) override;
      93             : 
      94             : private:
      95             :   /**
      96             :    * Data stored on a per-element basis used to compute element Schur complements and their
      97             :    * applications to vectors
      98             :    */
      99             :   struct DofData
     100             :   {
     101             :     /// A map from the global degree of freedom number for the full system (condensed + uncondensed)
     102             :     /// to an element local number. If this map is queried with a condensed dof, nothing will be
     103             :     /// found. The size of this container will be the number of uncondensed degrees of freedom whose
     104             :     /// basis functions are nonzero on the element
     105             :     std::unordered_map<dof_id_type, dof_id_type> uncondensed_global_to_local_map;
     106             :     /// A map from the global degree of freedom number for the full system (condensed + uncondensed)
     107             :     /// to an element local number. If this map is queried with an uncondensed dof, nothing will be
     108             :     /// found. The size of this container will be the number of condensed degrees of freedom whose
     109             :     /// basis functions are nonzero on the element
     110             :     std::unordered_map<dof_id_type, dof_id_type> condensed_global_to_local_map;
     111             :     /// The parent-space indices of the uncondensed and condensed degrees of freedom, by element
     112             :     /// local number
     113             :     std::vector<dof_id_type> uncondensed_parent_dofs;
     114             :     std::vector<dof_id_type> condensed_parent_dofs;
     115             :   };
     116             : 
     117             :   /// Friend the static condensation matrix class so they can inspect our degree of freedom data
     118             :   friend class StaticCondensation;
     119             : 
     120             :   /// A map from element ID to Schur complement data
     121             :   std::unordered_map<dof_id_type, DofData> _elem_to_dof_data;
     122             : 
     123             :   /// Variables for which we will keep all dofs
     124             :   std::unordered_set<unsigned int> _uncondensed_vars;
     125             : };
     126             : 
     127             : inline void
     128          16 : StaticCondensationDofMap::dont_condense_vars(const std::unordered_set<unsigned int> & vars)
     129             : {
     130          16 :   _uncondensed_vars.insert(vars.begin(), vars.end());
     131          16 : }
     132             : }
     133             : 
     134             : #endif // LIBMESH_STATIC_CONDENSATION_DOF_MAP_H