petsc_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_PETSC_LINEAR_SOLVER_H
#define LIBMESH_PETSC_LINEAR_SOLVER_H

#include "libmesh/libmesh_config.h"

#ifdef LIBMESH_HAVE_PETSC

#include "libmesh/petsc_macro.h"
#include "libmesh/petsc_solver_exception.h"
#include "libmesh/wrapped_petsc.h"

// Petsc include files.
#ifdef I
# define LIBMESH_SAW_I
#endif
#include <petscksp.h>
#ifndef LIBMESH_SAW_I
# undef I // Avoid complex.h contamination
#endif

// Local includes
#include "libmesh/linear_solver.h"

// C++ includes
#include <cstddef>
#include <vector>
#include <memory>

//--------------------------------------------------------------------
// Functions with C linkage to pass to PETSc.  PETSc will call these
// methods as needed for preconditioning
//
// Since they must have C linkage they have no knowledge of a namespace.
// Give them an obscure name to avoid namespace pollution.
extern "C"
{
  PetscErrorCode libmesh_petsc_preconditioner_setup (PC);

  PetscErrorCode libmesh_petsc_preconditioner_apply(PC, Vec x, Vec y);

#if LIBMESH_ENABLE_DEPRECATED

  PetscErrorCode __libmesh_petsc_preconditioner_setup (PC);

  PetscErrorCode __libmesh_petsc_preconditioner_apply(PC, Vec x, Vec y);
#endif
} // end extern "C"


namespace libMesh
{

// forward declarations
template <typename T> class PetscMatrixBase;

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

  virtual ~PetscLinearSolver () = default;

  virtual void clear () override;

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

  void init (PetscMatrixBase<T> * matrix,
             const char * name = nullptr);

  virtual void init_names (const System &) override;

  virtual void restrict_solve_to (const std::vector<unsigned int> * const dofs,
                                  const SubsetSolveMode subset_solve_mode=SUBSET_ZERO) override;

  virtual std::pair<unsigned int, Real>
  solve (SparseMatrix<T> & matrix_in,
         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
  {
    return this->solve(matrix_in, matrix_in, solution_in, rhs_in, tol, m_its);
  }


  virtual std::pair<unsigned int, Real>
  adjoint_solve (SparseMatrix<T> & matrix_in,
                 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 (SparseMatrix<T> & matrix,
         SparseMatrix<T> & preconditioner,
         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;

  PC pc() { this->init(); return _pc; }

  KSP ksp();

  void get_residual_history(std::vector<double> & hist);

  Real get_initial_residual();

  virtual LinearConvergenceReason get_converged_reason() const override;

private:

  typedef PetscErrorCode (*ksp_solve_func_type)(KSP,Vec,Vec);

  /*
   * Helper function to run solve() and adjoint_solve()
   */
  virtual std::pair<unsigned int, Real>
  solve_common (SparseMatrix<T> & matrix_in,
                SparseMatrix<T> & precond_in,
                NumericVector<T> & solution_in,
                NumericVector<T> & rhs_in,
                const double rel_tol,
                const double abs_tol,
                const unsigned int m_its,
                ksp_solve_func_type solve_func);

  /*
   * Helper function to run ShellMatrix solve() with or without a
   * separate preconditioner matrix
   */
  virtual std::pair<unsigned int, Real>
  shell_solve_common (const ShellMatrix<T> & shell_matrix,
                      PetscMatrixBase<T> * precond_matrix,
                      NumericVector<T> & solution_in,
                      NumericVector<T> & rhs_in,
                      const double rel_tol,
                      const double abs_tol,
                      const unsigned int m_its);

  /*
   * Helper function for the helper functions
   */
  std::pair<unsigned int, Real>
  solve_base (SparseMatrix<T> * matrix,
              PetscMatrixBase<T> * precond,
              Mat mat,
              NumericVector<T> & solution_in,
              NumericVector<T> & rhs_in,
              const double rel_tol,
              const double abs_tol,
              const unsigned int m_its,
              ksp_solve_func_type solve_func);


  void set_petsc_solver_type ();

  static PetscErrorCode _petsc_shell_matrix_mult(Mat mat, Vec arg, Vec dest);

  static PetscErrorCode _petsc_shell_matrix_mult_add(Mat mat, Vec arg, Vec add, Vec dest);

  static PetscErrorCode _petsc_shell_matrix_get_diagonal(Mat mat, Vec dest);

  PC _pc;

  WrappedPetsc<KSP> _ksp;

  WrappedPetsc<IS> _restrict_solve_to_is;

  WrappedPetsc<IS> _restrict_solve_to_is_complement;

  PetscInt restrict_solve_to_is_local_size() const;

  void create_complement_is (const NumericVector<T> & vec_in);

  SubsetSolveMode _subset_solve_mode;
};

} // namespace libMesh


#endif // #ifdef LIBMESH_HAVE_PETSC
#endif // LIBMESH_PETSC_LINEAR_SOLVER_H