static_condensation_dof_map.h

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// The libMesh Finite Element Library.
// Copyright (C) 2002-2026 Benjamin S. Kirk, John W. Peterson, Roy H. Stogner

// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.

// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

#ifndef LIBMESH_STATIC_CONDENSATION_DOF_MAP_H
#define LIBMESH_STATIC_CONDENSATION_DOF_MAP_H

#include "libmesh/libmesh_config.h"

#include "libmesh/id_types.h"
#include "libmesh/libmesh_common.h"
#include "libmesh/dof_map_base.h"
#include "libmesh/variable.h"
#include "libmesh/sparsity_pattern.h"
#include "libmesh/utility.h"

#include <unordered_map>
#include <memory>
#include <vector>

namespace libMesh
{
class MeshBase;
class System;
class DofMap;
class Elem;

class StaticCondensationDofMap : public DofMapBase
{
public:
  StaticCondensationDofMap(MeshBase & mesh, System & system, const DofMap & dof_map);
  virtual ~StaticCondensationDofMap();

  //
  // Unique methods
  //

  void reinit();

  void dont_condense_vars(const std::unordered_set<unsigned int> & vars);

  const std::unordered_set<unsigned int> & uncondensed_vars() const { return _uncondensed_vars; }

  virtual unsigned int n_variables() const override;

  virtual const Variable & variable(const unsigned int c) const override;

  virtual void dof_indices(const Elem * const elem,
                           std::vector<dof_id_type> & di,
                           const unsigned int vn,
                           int p_level = -12345) const override;

  virtual void dof_indices(const Node * const node,
                           std::vector<dof_id_type> & di,
                           const unsigned int vn) const override;

  /*
   * @returns The dummyish reduced system
   */
  const System & reduced_system() const;

  /*
   * @returns The mesh
   */
  const MeshBase & mesh () const { return _mesh; }

  bool initialized() const { return _sc_is_initialized; }

  virtual void clear() override;

  dof_id_type get_reduced_from_global_constraint_dof(dof_id_type full_dof) const;

private:
  void add_uncondensed_dof_plus_constraint_dofs(
      dof_id_type full_dof_number,
      bool involved_in_constraints,
      std::unordered_map<dof_id_type, dof_id_type> & uncondensed_global_to_local_map,
      std::unordered_set<dof_id_type> & local_uncondensed_dofs_set,
      std::unordered_map<processor_id_type, std::unordered_set<dof_id_type>> &
          nonlocal_uncondensed_dofs,
      std::vector<dof_id_type> & elem_uncondensed_dofs,
      dof_id_type & uncondensed_local_dof_number,
      std::unordered_set<dof_id_type> & constraint_dofs);

  void add_uncondensed_dof(
      dof_id_type full_dof_number,
      bool involved_in_constraints,
      std::unordered_map<dof_id_type, dof_id_type> & uncondensed_global_to_local_map,
      std::unordered_set<dof_id_type> & local_uncondensed_dofs_set,
      std::unordered_map<processor_id_type, std::unordered_set<dof_id_type>> &
          nonlocal_uncondensed_dofs,
      std::vector<dof_id_type> & elem_uncondensed_dofs,
      dof_id_type & uncondensed_local_dof_number,
      std::unordered_set<dof_id_type> & constraint_dofs);

  struct DofData
  {
    std::vector<std::vector<dof_id_type>> reduced_space_indices;

    std::unordered_map<dof_id_type, dof_id_type> uncondensed_global_to_local_map;
    std::unordered_map<dof_id_type, dof_id_type> condensed_global_to_local_map;
  };

  friend class StaticCondensation;

  std::unordered_map<dof_id_type, DofData> _elem_to_dof_data;

  std::vector<dof_id_type> _local_uncondensed_dofs;

  MeshBase & _mesh;
  System & _system;
  const DofMap & _dof_map;

  std::unordered_set<unsigned int> _uncondensed_vars;

  bool _sc_is_initialized;

  std::vector<Variable> _reduced_vars;

  System * _reduced_system;

  std::unique_ptr<SparsityPattern::Build> _reduced_sp;

  std::vector<dof_id_type> _reduced_nnz;

  std::vector<dof_id_type> _reduced_noz;

  std::unordered_map<dof_id_type, dof_id_type> _full_to_reduced_constraint_dofs;
};

inline void
StaticCondensationDofMap::dont_condense_vars(const std::unordered_set<unsigned int> & vars)
{
  _uncondensed_vars.insert(vars.begin(), vars.end());
}

inline const System & StaticCondensationDofMap::reduced_system() const
{
  libmesh_assert(_reduced_system);
  return *_reduced_system;
}

inline dof_id_type
StaticCondensationDofMap::get_reduced_from_global_constraint_dof(const dof_id_type full_dof) const
{
  return libmesh_map_find(_full_to_reduced_constraint_dofs, full_dof);
}

}

#endif // LIBMESH_STATIC_CONDENSATION_DOF_MAP_H