eigen_sparse_linear_solver.h

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// The libMesh Finite Element Library.
// Copyright (C) 2002-2025 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_EIGEN_SPARSE_LINEAR_SOLVER_H
#define LIBMESH_EIGEN_SPARSE_LINEAR_SOLVER_H

#include "libmesh/libmesh_common.h"

#ifdef LIBMESH_HAVE_EIGEN

// Eigen includes

// Local includes
#include "libmesh/linear_solver.h"
#include "libmesh/eigen_sparse_vector.h"
#include "libmesh/eigen_sparse_matrix.h"
#include "libmesh/enum_convergence_flags.h" // The build_map() function uses these.


namespace libMesh
{

template <typename T>
class EigenSparseLinearSolver : public LinearSolver<T>
{
public:
  EigenSparseLinearSolver (const libMesh::Parallel::Communicator & comm_in);

  ~EigenSparseLinearSolver ();

  virtual void clear () override;

  virtual void init (const char * name=nullptr) override;

  virtual std::pair<unsigned int, Real>
  solve (SparseMatrix<T> & matrix,
         NumericVector<T> & solution,
         NumericVector<T> & rhs,
         const std::optional<double> tol = std::nullopt,
         const std::optional<unsigned int> m_its = std::nullopt) override;

  virtual std::pair<unsigned int, Real>
  adjoint_solve (SparseMatrix<T> & matrix,
                 NumericVector<T> & solution,
                 NumericVector<T> & rhs,
                 const std::optional<double> tol = std::nullopt,
                 const std::optional<unsigned int> m_its = std::nullopt) override;

  virtual std::pair<unsigned int, Real>
  solve (SparseMatrix<T> & matrix,
         SparseMatrix<T> & pc,
         NumericVector<T> & solution,
         NumericVector<T> & rhs,
         const std::optional<double> tol = std::nullopt,
         const std::optional<unsigned int> m_its = std::nullopt) override;

  virtual std::pair<unsigned int, Real>
  solve (const ShellMatrix<T> & shell_matrix,
         NumericVector<T> & solution_in,
         NumericVector<T> & rhs_in,
         const std::optional<double> tol = std::nullopt,
         const std::optional<unsigned int> m_its = std::nullopt) override;

  virtual std::pair<unsigned int, Real>
  solve (const ShellMatrix<T> & shell_matrix,
         const SparseMatrix<T> & precond_matrix,
         NumericVector<T> & solution_in,
         NumericVector<T> & rhs_in,
         const std::optional<double> tol = std::nullopt,
         const std::optional<unsigned int> m_its = std::nullopt) override;

  virtual LinearConvergenceReason get_converged_reason() const override;

private:

  void set_eigen_preconditioner_type ();

  Eigen::ComputationInfo _comp_info;

  static std::map<Eigen::ComputationInfo, LinearConvergenceReason> _convergence_reasons;

  static std::map<Eigen::ComputationInfo, LinearConvergenceReason> build_map()
  {
    std::map<Eigen::ComputationInfo, LinearConvergenceReason> ret;
    ret[Eigen::Success]        = CONVERGED_ITS;
    ret[Eigen::NumericalIssue] = DIVERGED_BREAKDOWN;
    ret[Eigen::NoConvergence]  = DIVERGED_ITS;
    ret[Eigen::InvalidInput]   = DIVERGED_NULL;
    return ret;
  }
};



// Call the class-static function to define the class-static member.
// Since it's a template class, you actually do this in the header,
// not the source file.
template <typename T>
std::map<Eigen::ComputationInfo, LinearConvergenceReason>
EigenSparseLinearSolver<T>::_convergence_reasons = EigenSparseLinearSolver<T>::build_map();



template <typename T>
inline
EigenSparseLinearSolver<T>::~EigenSparseLinearSolver ()
{
  this->clear ();
}



template <typename T>
inline
std::pair<unsigned int, Real>
EigenSparseLinearSolver<T>::solve (SparseMatrix<T> &,
                                   SparseMatrix<T> &,
                                   NumericVector<T> &,
                                   NumericVector<T> &,
                                   const std::optional<double>,
                                   const std::optional<unsigned int>)
{
  libmesh_error_msg("ERROR: Eigen does not support a user-supplied preconditioner!");

  return std::pair<unsigned int, Real>();
}

} // namespace libMesh

#endif // #ifdef LIBMESH_HAVE_EIGEN
#endif // LIBMESH_EIGEN_SPARSE_LINEAR_SOLVER_H