Ifpack_ex_BlockRelaxation.cpp

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//       Ifpack: Object-Oriented Algebraic Preconditioner Package
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#include "Ifpack_ConfigDefs.h"

#ifdef HAVE_MPI
#include "Epetra_MpiComm.h"
#else
#include "Epetra_SerialComm.h"
#endif
#include "Epetra_CrsMatrix.h"
#include "Epetra_MultiVector.h"
#include "Epetra_LinearProblem.h"
#include "Galeri_Maps.h"
#include "Galeri_CrsMatrices.h"
#include "Teuchos_ParameterList.hpp"
#include "Teuchos_RefCountPtr.hpp"
#include "AztecOO.h"
#include "Ifpack_AdditiveSchwarz.h"
#include "Ifpack_PointRelaxation.h"
#include "Ifpack_BlockRelaxation.h"
#include "Ifpack_SparseContainer.h"
#include "Ifpack_Amesos.h"

int main(int argc, char *argv[])
{
  // initialize MPI and Epetra communicator
#ifdef HAVE_MPI
  MPI_Init(&argc,&argv);
  Epetra_MpiComm Comm( MPI_COMM_WORLD );
#else
  Epetra_SerialComm Comm;
#endif

  Teuchos::ParameterList GaleriList;

  // The problem is defined on a 2D grid, global size is nx * nx.
  int nx = 30; 
  GaleriList.set("nx", nx);
  GaleriList.set("ny", nx * Comm.NumProc());
  GaleriList.set("mx", 1);
  GaleriList.set("my", Comm.NumProc());
  Teuchos::RefCountPtr<Epetra_Map> Map = Teuchos::rcp( Galeri::CreateMap("Cartesian2D", Comm, GaleriList) );
  Teuchos::RefCountPtr<Epetra_RowMatrix> A = Teuchos::rcp( Galeri::CreateCrsMatrix("Laplace2D", &*Map, GaleriList) );

  // =============================================================== //
  // B E G I N N I N G   O F   I F P A C K   C O N S T R U C T I O N //
  // =============================================================== //

  Teuchos::ParameterList List;

  // builds an Ifpack_AdditiveSchwarz. This is templated with
  // the local solvers, in this case Ifpack_BlockRelaxation.
  // Ifpack_BlockRelaxation requires as a templated a container
  // class. A container defines
  // how to store the diagonal blocks. Two choices are available:
  // Ifpack_DenseContainer (to store them as dense block,
  // than use LAPACK' factorization to apply the inverse of
  // each block), of Ifpack_SparseContainer (to store
  // the diagonal block as Epetra_CrsMatrix's). 
  // 
  // Here, we use Ifpack_SparseContainer, which in turn is
  // templated with the class to use to apply the inverse
  // of each block. For example, we can use Ifpack_Amesos.
 
  // We still have to decide the overlap among the processes,
  // and the overlap among the blocks. The two values
  // can be different. The overlap among the blocks is
  // considered only if block Jacobi is used.
  int OverlapProcs = 2;
  int OverlapBlocks = 0;

  // define the block below to use dense containers
#if 0
  Ifpack_AdditiveSchwarz<Ifpack_BlockRelaxation<Ifpack_DenseContainer> > Prec(A, OverlapProcs);
#else
  Ifpack_AdditiveSchwarz<Ifpack_BlockRelaxation<Ifpack_SparseContainer<Ifpack_Amesos> > > Prec(&*A, OverlapProcs);
#endif

  List.set("relaxation: type", "symmetric Gauss-Seidel");
  List.set("partitioner: overlap", OverlapBlocks);
#ifdef HAVE_IFPACK_METIS
  // use METIS to create the blocks. This requires --enable-ifpack-metis.
  // If METIS is not installed, the user may select "linear". 
  List.set("partitioner: type", "metis");
#else
  // or a simple greedy algorithm is METIS is not enabled
  List.set("partitioner: type", "greedy");
#endif
  // defines here the number of local blocks. If 1,
  // and only one process is used in the computation, then
  // the preconditioner must converge in one iteration. 
  List.set("partitioner: local parts", 4);

  // sets the parameters
  IFPACK_CHK_ERR(Prec.SetParameters(List));

  // initialize the preconditioner. 
  IFPACK_CHK_ERR(Prec.Initialize());

  // Builds the preconditioners.
  IFPACK_CHK_ERR(Prec.Compute());

  // =================================================== //
  // E N D   O F   I F P A C K   C O N S T R U C T I O N //
  // =================================================== //

  // At this point, we need some additional objects
  // to define and solve the linear system.

  // defines LHS and RHS
  Epetra_Vector LHS(A->OperatorDomainMap());
  Epetra_Vector RHS(A->OperatorDomainMap());

  LHS.PutScalar(0.0);
  RHS.Random();

  // need an Epetra_LinearProblem to define AztecOO solver
  Epetra_LinearProblem Problem(&*A,&LHS,&RHS);

  // now we can allocate the AztecOO solver
  AztecOO Solver(Problem);

  // specify solver
  Solver.SetAztecOption(AZ_solver,AZ_cg);
  Solver.SetAztecOption(AZ_output,32);

  // HERE WE SET THE IFPACK PRECONDITIONER
  Solver.SetPrecOperator(&Prec);

  // .. and here we solve
  // NOTE: with one process, the solver must converge in
  // one iteration.
  Solver.Iterate(1550,1e-5);

#ifdef HAVE_MPI
  MPI_Finalize() ; 
#endif

  return(EXIT_SUCCESS);
}