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//
// Copyright (C) 1999 - 2016 by the deal.II authors
//
// This file is part of the deal.II library.
//
// The deal.II library is free software; you can use it, 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.
// The full text of the license can be found in the file LICENSE at
// the top level of the deal.II distribution.
//
// ---------------------------------------------------------------------
#ifndef dealii__multigrid_h
#define dealii__multigrid_h
#include <deal.II/base/config.h>
#include <deal.II/base/subscriptor.h>
#include <deal.II/base/smartpointer.h>
#include <deal.II/dofs/dof_handler.h>
#include <deal.II/lac/sparse_matrix.h>
#include <deal.II/lac/vector.h>
#include <deal.II/multigrid/mg_base.h>
#include <deal.II/base/mg_level_object.h>
#include <vector>
DEAL_II_NAMESPACE_OPEN
/*!@addtogroup mg */
/*@{*/
/**
* Implementation of the multigrid method.
*
* @warning multigrid on locally refined meshes only works with
* <b>discontinuous finite elements</b> right now. It is not clear, whether
* the paradigm of local smoothing we use is applicable to continuous elements
* with hanging nodes; in fact, most people you meet on conferences seem to
* deny this.
*
* The function which starts a multigrid cycle on the finest level is cycle().
* Depending on the cycle type chosen with the constructor (see enum Cycle),
* this function triggers one of the cycles level_v_step() or level_step(),
* where the latter one can do different types of cycles.
*
* Using this class, it is expected that the right hand side has been
* converted from a vector living on the locally finest level to a multilevel
* vector. This is a nontrivial operation, usually initiated automatically by
* the class PreconditionMG and performed by the classes derived from
* MGTransferBase.
*
* @note The interface of this class is still very clumsy. In particular, you
* will have to set up quite a few auxiliary objects before you can use it.
* Unfortunately, it seems that this can be avoided only be restricting the
* flexibility of this class in an unacceptable way.
*
* @author Guido Kanschat, 1999 - 2005
*/
template <typename VectorType>
class Multigrid : public Subscriptor
{
public:
/**
* List of implemented cycle types.
*/
enum Cycle
{
/// The V-cycle
v_cycle,
/// The W-cycle
w_cycle,
/// The F-cycle
f_cycle
};
typedef VectorType vector_type;
typedef const VectorType const_vector_type;
/**
* Constructor. The DoFHandler is used to determine the highest possible
* level. <tt>transfer</tt> is an object performing prolongation and
* restriction.
*
* This function already initializes the vectors which will be used later in
* the course of the computations. You should therefore create objects of
* this type as late as possible.
*/
template <int dim>
Multigrid(const DoFHandler<dim> &mg_dof_handler,
const MGMatrixBase<VectorType> &matrix,
const MGCoarseGridBase<VectorType> &coarse,
const MGTransferBase<VectorType> &transfer,
const MGSmootherBase<VectorType> &pre_smooth,
const MGSmootherBase<VectorType> &post_smooth,
Cycle cycle = v_cycle);
/**
* Experimental constructor for cases in which no DoFHandler is available.
*
* @warning Not intended for general use.
*/
Multigrid(const unsigned int minlevel,
const unsigned int maxlevel,
const MGMatrixBase<VectorType> &matrix,
const MGCoarseGridBase<VectorType> &coarse,
const MGTransferBase<VectorType> &transfer,
const MGSmootherBase<VectorType> &pre_smooth,
const MGSmootherBase<VectorType> &post_smooth,
Cycle cycle = v_cycle);
/**
* Reinit this class according to #minlevel and #maxlevel.
*/
void reinit (const unsigned int minlevel,
const unsigned int maxlevel);
/**
* Execute one multigrid cycle. The type of cycle is selected by the
* constructor argument cycle. See the enum Cycle for available types.
*/
void cycle ();
/**
* Execute one step of the V-cycle algorithm. This function assumes, that
* the multilevel vector #defect is filled with the residual of an outer
* defect correction scheme. This is usually taken care of by
* PreconditionMG). After vcycle(), the result is in the multilevel vector
* #solution. See <tt>copy_*_mg</tt> in the MGTools namespace if you want to
* use these vectors yourself.
*
* The actual work for this function is done in level_v_step().
*/
void vcycle ();
/**
* Set additional matrices to correct residual computation at refinement
* edges. Since we only smoothen in the interior of the refined part of the
* mesh, the coupling across the refinement edge is missing. This coupling
* is provided by these two matrices.
*
* @note While <tt>edge_out.vmult</tt> is used, for the second argument, we
* use <tt>edge_in.Tvmult</tt>. Thus, <tt>edge_in</tt> should be assembled
* in transposed form. This saves a second sparsity pattern for
* <tt>edge_in</tt>. In particular, for symmetric operators, both arguments
* can refer to the same matrix, saving assembling of one of them.
*/
void set_edge_matrices (const MGMatrixBase<VectorType> &edge_out,
const MGMatrixBase<VectorType> &edge_in);
/**
* Set additional matrices to correct residual computation at refinement
* edges. These matrices originate from discontinuous Galerkin methods (see
* FE_DGQ etc.), where they correspond to the edge fluxes at the refinement
* edge between two levels.
*
* @note While <tt>edge_down.vmult</tt> is used, for the second argument, we
* use <tt>edge_up.Tvmult</tt>. Thus, <tt>edge_up</tt> should be assembled
* in transposed form. This saves a second sparsity pattern for
* <tt>edge_up</tt>. In particular, for symmetric operators, both arguments
* can refer to the same matrix, saving assembling of one of them.
*/
void set_edge_flux_matrices (const MGMatrixBase<VectorType> &edge_down,
const MGMatrixBase<VectorType> &edge_up);
/**
* Return the finest level for multigrid.
*/
unsigned int get_maxlevel() const;
/**
* Return the coarsest level for multigrid.
*/
unsigned int get_minlevel() const;
/**
* Set the highest level for which the multilevel method is performed. By
* default, this is the finest level of the Triangulation; therefore, this
* function will only accept arguments smaller than the current #maxlevel
* and not smaller than the current #minlevel.
*/
void set_maxlevel (const unsigned int);
/**
* Set the coarsest level for which the multilevel method is performed. By
* default, this is zero. Accepted are non-negative values not larger than
* the current #maxlevel.
*
* If <tt>relative</tt> is <tt>true</tt>, then this function determines the
* number of levels used, that is, it sets #minlevel to
* #maxlevel-<tt>level</tt>.
*
* @note The mesh on the coarsest level must cover the whole domain. There
* may not be hanging nodes on #minlevel.
*
* @note If #minlevel is set to a nonzero value, do not forget to adjust
* your coarse grid solver!
*/
void set_minlevel (const unsigned int level,
bool relative = false);
/**
* Chance #cycle_type used in cycle().
*/
void set_cycle(Cycle);
/**
* Set the debug level. Higher values will create more debugging output
* during the multigrid cycles.
*/
void set_debug (const unsigned int);
private:
/**
* The V-cycle multigrid method. <tt>level</tt> is the level the function
* starts on. It will usually be called for the highest level from outside,
* but will then call itself recursively for <tt>level-1</tt>, unless we are
* on #minlevel where the coarse grid solver solves the problem exactly.
*/
void level_v_step (const unsigned int level);
/**
* The actual W-cycle or F-cycle multigrid method. <tt>level</tt> is the
* level the function starts on. It will usually be called for the highest
* level from outside, but will then call itself recursively for
* <tt>level-1</tt>, unless we are on #minlevel where the coarse grid solver
* solves the problem exactly.
*/
void level_step (const unsigned int level, Cycle cycle);
/**
* Cycle type performed by the method cycle().
*/
Cycle cycle_type;
/**
* Level for coarse grid solution.
*/
unsigned int minlevel;
/**
* Highest level of cells.
*/
unsigned int maxlevel;
public:
/**
* Input vector for the cycle. Contains the defect of the outer method
* projected to the multilevel vectors.
*/
MGLevelObject<VectorType> defect;
/**
* The solution update after the multigrid step.
*/
MGLevelObject<VectorType> solution;
private:
/**
* Auxiliary vector.
*/
MGLevelObject<VectorType> t;
/**
* Auxiliary vector for W- and F-cycles. Left uninitialized in V-cycle.
*/
MGLevelObject<VectorType> defect2;
/**
* The matrix for each level.
*/
SmartPointer<const MGMatrixBase<VectorType>,Multigrid<VectorType> > matrix;
/**
* The matrix for each level.
*/
SmartPointer<const MGCoarseGridBase<VectorType>,Multigrid<VectorType> > coarse;
/**
* Object for grid tranfer.
*/
SmartPointer<const MGTransferBase<VectorType>,Multigrid<VectorType> > transfer;
/**
* The pre-smoothing object.
*/
SmartPointer<const MGSmootherBase<VectorType>,Multigrid<VectorType> > pre_smooth;
/**
* The post-smoothing object.
*/
SmartPointer<const MGSmootherBase<VectorType>,Multigrid<VectorType> > post_smooth;
/**
* Edge matrix from the interior of the refined part to the refinement edge.
*
* @note Only <tt>vmult</tt> is used for these matrices.
*/
SmartPointer<const MGMatrixBase<VectorType> > edge_out;
/**
* Transpose edge matrix from the refinement edge to the interior of the
* refined part.
*
* @note Only <tt>Tvmult</tt> is used for these matrices.
*/
SmartPointer<const MGMatrixBase<VectorType> > edge_in;
/**
* Edge matrix from fine to coarse.
*
* @note Only <tt>vmult</tt> is used for these matrices.
*/
SmartPointer<const MGMatrixBase<VectorType>,Multigrid<VectorType> > edge_down;
/**
* Transpose edge matrix from coarse to fine.
*
* @note Only <tt>Tvmult</tt> is used for these matrices.
*/
SmartPointer<const MGMatrixBase<VectorType>,Multigrid<VectorType> > edge_up;
/**
* Level for debug output. Defaults to zero and can be set by set_debug().
*/
unsigned int debug;
template<int dim, class OtherVectorType, class TRANSFER> friend class PreconditionMG;
};
/**
* Multi-level preconditioner. Here, we collect all information needed for
* multi-level preconditioning and provide the standard interface for LAC
* iterative methods.
*
* Furthermore, it needs functions <tt>void copy_to_mg(const VectorType&)</tt>
* to store @p src in the right hand side of the multi-level method and
* <tt>void copy_from_mg(VectorType&)</tt> to store the result of the v-cycle
* in @p dst.
*
* @author Guido Kanschat, 1999, 2000, 2001, 2002
*/
template<int dim, typename VectorType, class TRANSFER>
class PreconditionMG : public Subscriptor
{
public:
/**
* Constructor. Arguments are the multigrid object, pre-smoother, post-
* smoother and coarse grid solver.
*/
PreconditionMG(const DoFHandler<dim> &dof_handler,
Multigrid<VectorType> &mg,
const TRANSFER &transfer);
/**
* Dummy function needed by other classes.
*/
bool empty () const;
/**
* Preconditioning operator. Calls the @p vcycle function of the @p MG
* object passed to the constructor.
*
* This is the operator used by LAC iterative solvers.
*/
template<class OtherVectorType>
void vmult (OtherVectorType &dst,
const OtherVectorType &src) const;
/**
* Preconditioning operator. Calls the @p vcycle function of the @p MG
* object passed to the constructor.
*/
template<class OtherVectorType>
void vmult_add (OtherVectorType &dst,
const OtherVectorType &src) const;
/**
* Tranposed preconditioning operator.
*
* Not implemented, but the definition may be needed.
*/
template<class OtherVectorType>
void Tvmult (OtherVectorType &dst,
const OtherVectorType &src) const;
/**
* Tranposed preconditioning operator.
*
* Not implemented, but the definition may be needed.
*/
template<class OtherVectorType>
void Tvmult_add (OtherVectorType &dst,
const OtherVectorType &src) const;
private:
/**
* Associated @p DoFHandler.
*/
SmartPointer<const DoFHandler<dim>,PreconditionMG<dim,VectorType,TRANSFER> > dof_handler;
/**
* The multigrid object.
*/
SmartPointer<Multigrid<VectorType>,PreconditionMG<dim,VectorType,TRANSFER> > multigrid;
/**
* Object for grid tranfer.
*/
SmartPointer<const TRANSFER,PreconditionMG<dim,VectorType,TRANSFER> > transfer;
};
/*@}*/
#ifndef DOXYGEN
/* --------------------------- inline functions --------------------- */
template <typename VectorType>
template <int dim>
Multigrid<VectorType>::Multigrid (const DoFHandler<dim> &mg_dof_handler,
const MGMatrixBase<VectorType> &matrix,
const MGCoarseGridBase<VectorType> &coarse,
const MGTransferBase<VectorType> &transfer,
const MGSmootherBase<VectorType> &pre_smooth,
const MGSmootherBase<VectorType> &post_smooth,
Cycle cycle)
:
cycle_type(cycle),
minlevel(0),
maxlevel(mg_dof_handler.get_triangulation().n_global_levels()-1),
defect(minlevel,maxlevel),
solution(minlevel,maxlevel),
t(minlevel,maxlevel),
defect2(minlevel,maxlevel),
matrix(&matrix, typeid(*this).name()),
coarse(&coarse, typeid(*this).name()),
transfer(&transfer, typeid(*this).name()),
pre_smooth(&pre_smooth, typeid(*this).name()),
post_smooth(&post_smooth, typeid(*this).name()),
edge_down(0, typeid(*this).name()),
edge_up(0, typeid(*this).name()),
debug(0)
{}
template <typename VectorType>
inline
unsigned int
Multigrid<VectorType>::get_maxlevel () const
{
return maxlevel;
}
template <typename VectorType>
inline
unsigned int
Multigrid<VectorType>::get_minlevel () const
{
return minlevel;
}
/* --------------------------- inline functions --------------------- */
template<int dim, typename VectorType, class TRANSFER>
PreconditionMG<dim, VectorType, TRANSFER>
::PreconditionMG(const DoFHandler<dim> &dof_handler,
Multigrid<VectorType> &mg,
const TRANSFER &transfer)
:
dof_handler(&dof_handler),
multigrid(&mg),
transfer(&transfer)
{}
template<int dim, typename VectorType, class TRANSFER>
inline bool
PreconditionMG<dim, VectorType, TRANSFER>::empty () const
{
return false;
}
template<int dim, typename VectorType, class TRANSFER>
template<class OtherVectorType>
void
PreconditionMG<dim, VectorType, TRANSFER>::vmult
(OtherVectorType &dst,
const OtherVectorType &src) const
{
transfer->copy_to_mg(*dof_handler,
multigrid->defect,
src);
multigrid->cycle();
transfer->copy_from_mg(*dof_handler,
dst,
multigrid->solution);
}
template<int dim, typename VectorType, class TRANSFER>
template<class OtherVectorType>
void
PreconditionMG<dim, VectorType, TRANSFER>::vmult_add
(OtherVectorType &dst,
const OtherVectorType &src) const
{
transfer->copy_to_mg(*dof_handler,
multigrid->defect,
src);
multigrid->cycle();
transfer->copy_from_mg_add(*dof_handler,
dst,
multigrid->solution);
}
template<int dim, typename VectorType, class TRANSFER>
template<class OtherVectorType>
void
PreconditionMG<dim, VectorType, TRANSFER>::Tvmult
(OtherVectorType &,
const OtherVectorType &) const
{
Assert(false, ExcNotImplemented());
}
template<int dim, typename VectorType, class TRANSFER>
template<class OtherVectorType>
void
PreconditionMG<dim, VectorType, TRANSFER>::Tvmult_add
(OtherVectorType &,
const OtherVectorType &) const
{
Assert(false, ExcNotImplemented());
}
#endif // DOXYGEN
DEAL_II_NAMESPACE_CLOSE
#endif
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