mg_coarse.h

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// ------------------------------------------------------------------------
//
// SPDX-License-Identifier: LGPL-2.1-or-later
// Copyright (C) 2002 - 2023 by the deal.II authors
//
// This file is part of the deal.II library.
//
// Part of the source code is dual licensed under Apache-2.0 WITH
// LLVM-exception OR LGPL-2.1-or-later. Detailed license information
// governing the source code and code contributions can be found in
// LICENSE.md and CONTRIBUTING.md at the top level directory of deal.II.
//
// ------------------------------------------------------------------------
 
#ifndef dealii_mg_coarse_h
#define dealii_mg_coarse_h
 
 
#include <deal.II/base/config.h>
 
#include <deal.II/lac/full_matrix.h>
#include <deal.II/lac/householder.h>
#include <deal.II/lac/linear_operator.h>
 
#include <deal.II/multigrid/mg_base.h>
 
DEAL_II_NAMESPACE_OPEN
 
template <typename VectorType = Vector<double>>
class MGCoarseGridApplySmoother : public MGCoarseGridBase<VectorType>
{
public:
  MGCoarseGridApplySmoother();
 
  MGCoarseGridApplySmoother(const MGSmootherBase<VectorType> &coarse_smooth);
 
  void
  clear();
 
  void
  initialize(const MGSmootherBase<VectorType> &coarse_smooth);
 
  void
  operator()(const unsigned int level,
             VectorType        &dst,
             const VectorType  &src) const override;
 
private:
  ObserverPointer<const MGSmootherBase<VectorType>,
                  MGCoarseGridApplySmoother<VectorType>>
    coarse_smooth;
};
 
 
 
template <typename VectorType,
          typename SolverType,
          typename MatrixType,
          typename PreconditionerType>
class MGCoarseGridIterativeSolver : public MGCoarseGridBase<VectorType>
{
public:
  MGCoarseGridIterativeSolver();
 
  MGCoarseGridIterativeSolver(SolverType               &solver,
                              const MatrixType         &matrix,
                              const PreconditionerType &precondition);
 
  void
  initialize(SolverType               &solver,
             const MatrixType         &matrix,
             const PreconditionerType &precondition);
 
  void
  clear();
 
  virtual void
  operator()(const unsigned int level,
             VectorType        &dst,
             const VectorType  &src) const override;
 
private:
  ObserverPointer<SolverType,
                  MGCoarseGridIterativeSolver<VectorType,
                                              SolverType,
                                              MatrixType,
                                              PreconditionerType>>
    solver;
 
  ObserverPointer<const MatrixType,
                  MGCoarseGridIterativeSolver<VectorType,
                                              SolverType,
                                              MatrixType,
                                              PreconditionerType>>
    matrix;
 
  ObserverPointer<const PreconditionerType,
                  MGCoarseGridIterativeSolver<VectorType,
                                              SolverType,
                                              MatrixType,
                                              PreconditionerType>>
    preconditioner;
};
 
 
 
template <typename number = double, typename VectorType = Vector<number>>
class MGCoarseGridHouseholder : public MGCoarseGridBase<VectorType>
{
public:
  MGCoarseGridHouseholder(const FullMatrix<number> *A = nullptr);
 
  void
  initialize(const FullMatrix<number> &A);
 
  void
  operator()(const unsigned int level,
             VectorType        &dst,
             const VectorType  &src) const override;
 
private:
  Householder<number> householder;
};
 
template <typename number = double, typename VectorType = Vector<number>>
class MGCoarseGridSVD : public MGCoarseGridBase<VectorType>
{
public:
  MGCoarseGridSVD() = default;
 
  void
  initialize(const FullMatrix<number> &A, const double threshold = 0);
 
  void
  operator()(const unsigned int level,
             VectorType        &dst,
             const VectorType  &src) const;
 
  void
  log() const;
 
private:
  LAPACKFullMatrix<number> matrix;
};
 
#ifndef DOXYGEN
/* ------------------ Functions for MGCoarseGridApplySmoother -----------*/
template <typename VectorType>
MGCoarseGridApplySmoother<VectorType>::MGCoarseGridApplySmoother()
  : coarse_smooth(nullptr)
{}
 
template <typename VectorType>
MGCoarseGridApplySmoother<VectorType>::MGCoarseGridApplySmoother(
  const MGSmootherBase<VectorType> &coarse_smooth)
  : coarse_smooth(nullptr)
{
  initialize(coarse_smooth);
}
 
 
template <typename VectorType>
void
MGCoarseGridApplySmoother<VectorType>::initialize(
  const MGSmootherBase<VectorType> &coarse_smooth_)
{
  coarse_smooth = ObserverPointer<const MGSmootherBase<VectorType>,
                                  MGCoarseGridApplySmoother<VectorType>>(
    &coarse_smooth_, typeid(*this).name());
}
 
 
template <typename VectorType>
void
MGCoarseGridApplySmoother<VectorType>::clear()
{
  coarse_smooth = nullptr;
}
 
 
template <typename VectorType>
void
MGCoarseGridApplySmoother<VectorType>::operator()(const unsigned int level,
                                                  VectorType        &dst,
                                                  const VectorType  &src) const
{
  coarse_smooth->apply(level, dst, src);
}
 
/* ------------------ Functions for MGCoarseGridIterativeSolver ------------ */
 
template <typename VectorType,
          typename SolverType,
          typename MatrixType,
          typename PreconditionerType>
MGCoarseGridIterativeSolver<VectorType,
                            SolverType,
                            MatrixType,
                            PreconditionerType>::MGCoarseGridIterativeSolver()
  : solver(0, typeid(*this).name())
  , matrix(0, typeid(*this).name())
  , preconditioner(0, typeid(*this).name())
{}
 
 
 
template <typename VectorType,
          typename SolverType,
          typename MatrixType,
          typename PreconditionerType>
MGCoarseGridIterativeSolver<VectorType,
                            SolverType,
                            MatrixType,
                            PreconditionerType>::
  MGCoarseGridIterativeSolver(SolverType               &solver,
                              const MatrixType         &matrix,
                              const PreconditionerType &preconditioner)
  : solver(&solver, typeid(*this).name())
  , matrix(&matrix, typeid(*this).name())
  , preconditioner(&preconditioner, typeid(*this).name())
{}
 
 
 
template <typename VectorType,
          typename SolverType,
          typename MatrixType,
          typename PreconditionerType>
void
MGCoarseGridIterativeSolver<
  VectorType,
  SolverType,
  MatrixType,
  PreconditionerType>::initialize(SolverType               &solver_,
                                  const MatrixType         &matrix_,
                                  const PreconditionerType &preconditioner_)
{
  solver         = &solver_;
  matrix         = &matrix_;
  preconditioner = &preconditioner_;
}
 
 
 
template <typename VectorType,
          typename SolverType,
          typename MatrixType,
          typename PreconditionerType>
void
MGCoarseGridIterativeSolver<VectorType,
                            SolverType,
                            MatrixType,
                            PreconditionerType>::clear()
{
  solver         = 0;
  matrix         = 0;
  preconditioner = 0;
}
 
 
 
namespace internal
{
  namespace MGCoarseGridIterativeSolver
  {
    template <typename VectorType,
              typename SolverType,
              typename MatrixType,
              typename PreconditionerType,
              std::enable_if_t<
                std::is_same_v<VectorType, typename SolverType::vector_type>,
                VectorType> * = nullptr>
    void
    solve(SolverType               &solver,
          const MatrixType         &matrix,
          const PreconditionerType &preconditioner,
          VectorType               &dst,
          const VectorType         &src)
    {
      solver.solve(matrix, dst, src, preconditioner);
    }
 
    template <typename VectorType,
              typename SolverType,
              typename MatrixType,
              typename PreconditionerType,
              std::enable_if_t<
                !std::is_same_v<VectorType, typename SolverType::vector_type>,
                VectorType> * = nullptr>
    void
    solve(SolverType               &solver,
          const MatrixType         &matrix,
          const PreconditionerType &preconditioner,
          VectorType               &dst,
          const VectorType         &src)
    {
      typename SolverType::vector_type src_;
      typename SolverType::vector_type dst_;
 
      src_ = src;
      dst_ = dst;
 
      solver.solve(matrix, dst_, src_, preconditioner);
 
      dst = dst_;
    }
  } // namespace MGCoarseGridIterativeSolver
} // namespace internal
 
 
 
template <typename VectorType,
          typename SolverType,
          typename MatrixType,
          typename PreconditionerType>
void
MGCoarseGridIterativeSolver<
  VectorType,
  SolverType,
  MatrixType,
  PreconditionerType>::operator()(const unsigned int /*level*/,
                                  VectorType       &dst,
                                  const VectorType &src) const
{
  Assert(solver != nullptr, ExcNotInitialized());
  Assert(matrix != nullptr, ExcNotInitialized());
  Assert(preconditioner != nullptr, ExcNotInitialized());
 
  dst = 0;
  internal::MGCoarseGridIterativeSolver::solve(
    *solver, *matrix, *preconditioner, dst, src);
}
 
 
 
/* ------------------ Functions for MGCoarseGridHouseholder ------------ */
 
template <typename number, typename VectorType>
MGCoarseGridHouseholder<number, VectorType>::MGCoarseGridHouseholder(
  const FullMatrix<number> *A)
{
  if (A != nullptr)
    householder.initialize(*A);
}
 
 
 
template <typename number, typename VectorType>
void
MGCoarseGridHouseholder<number, VectorType>::initialize(
  const FullMatrix<number> &A)
{
  householder.initialize(A);
}
 
 
 
template <typename number, typename VectorType>
void
MGCoarseGridHouseholder<number, VectorType>::operator()(
  const unsigned int /*level*/,
  VectorType       &dst,
  const VectorType &src) const
{
  householder.least_squares(dst, src);
}
 
//---------------------------------------------------------------------------
 
 
 
template <typename number, typename VectorType>
void
MGCoarseGridSVD<number, VectorType>::initialize(const FullMatrix<number> &A,
                                                double threshold)
{
  matrix.reinit(A.n_rows(), A.n_cols());
  matrix = A;
  matrix.compute_inverse_svd(threshold);
}
 
 
template <typename number, typename VectorType>
void
MGCoarseGridSVD<number, VectorType>::operator()(const unsigned int /*level*/,
                                                VectorType       &dst,
                                                const VectorType &src) const
{
  matrix.vmult(dst, src);
}
 
 
template <typename number, typename VectorType>
void
MGCoarseGridSVD<number, VectorType>::log() const
{
  const unsigned int n = std::min(matrix.n_rows(), matrix.n_cols());
 
  for (unsigned int i = 0; i < n; ++i)
    deallog << ' ' << matrix.singular_value(i);
  deallog << std::endl;
}
 
 
#endif // DOXYGEN
 
DEAL_II_NAMESPACE_CLOSE
 
#endif