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epetra/example/BlockGmres/BlockFlexGmresEpetraExFile.cpp

This is an example of how to use the Belos::BlockGmresSolMgr solver manager with flexible Gmres.

// @HEADER
// *****************************************************************************
// Belos: Block Linear Solvers Package
//
// Copyright 2004-2016 NTESS and the Belos contributors.
// SPDX-License-Identifier: BSD-3-Clause
// *****************************************************************************
// @HEADER
//
// This driver reads a problem from a file, which can be in Harwell-Boeing (*.hb),
// Matrix Market (*.mtx), or triplet format (*.triU, *.triS). The right-hand side
// from the problem, if it exists, will be used instead of multiple random
// right-hand-sides. The initial guesses are all set to zero. An ILU preconditioner
// is constructed using the Ifpack factory.
//
#include "BelosEpetraAdapter.hpp"
#include "EpetraExt_readEpetraLinearSystem.h"
#include "Epetra_Map.h"
#ifdef EPETRA_MPI
#include "Epetra_MpiComm.h"
#else
#include "Epetra_SerialComm.h"
#endif
#include "Epetra_CrsMatrix.h"
#include "Ifpack.h"
#include "Teuchos_StandardCatchMacros.hpp"
int main(int argc, char *argv[]) {
//
int MyPID = 0;
#ifdef EPETRA_MPI
// Initialize MPI
MPI_Init(&argc,&argv);
Epetra_MpiComm Comm(MPI_COMM_WORLD);
MyPID = Comm.MyPID();
#else
#endif
//
typedef double ST;
typedef SCT::magnitudeType MT;
typedef Epetra_MultiVector MV;
typedef Epetra_Operator OP;
using Teuchos::RCP;
using Teuchos::rcp;
bool success = false;
bool verbose = false;
try {
bool proc_verbose = false;
int frequency = -1; // frequency of status test output.
int blocksize = 1; // blocksize
int numrhs = 1; // number of right-hand sides to solve for
int maxrestarts = 15; // maximum number of restarts allowed
int maxiters = -1; // maximum number of iterations allowed per linear system
int maxsubspace = 25; // maximum number of blocks the solver can use for the subspace
std::string filename("orsirr1.hb");
MT tol = 1.0e-5; // relative residual tolerance
// Specify whether to use RHS as initial guess. If false, use zero.
bool useRHSAsInitialGuess = false;
cmdp.setOption("verbose","quiet",&verbose,"Print messages and results.");
cmdp.setOption("use-rhs","use-zero",&useRHSAsInitialGuess,"Use RHS as initial guess.");
cmdp.setOption("frequency",&frequency,"Solvers frequency for printing residuals (#iters).");
cmdp.setOption("filename",&filename,"Filename for test matrix. Acceptable file extensions: *.hb,*.mtx,*.triU,*.triS");
cmdp.setOption("tol",&tol,"Relative residual tolerance used by GMRES solver.");
cmdp.setOption("num-rhs",&numrhs,"Number of right-hand sides to be solved for.");
cmdp.setOption("block-size",&blocksize,"Block size used by GMRES.");
cmdp.setOption("max-iters",&maxiters,"Maximum number of iterations per linear system (-1 = adapted to problem/block size).");
cmdp.setOption("max-subspace",&maxsubspace,"Maximum number of blocks the solver can use for the subspace.");
cmdp.setOption("max-restarts",&maxrestarts,"Maximum number of restarts allowed for GMRES solver.");
return EXIT_FAILURE;
}
if (!verbose)
frequency = -1; // reset frequency if test is not verbose
//
// *************Get the problem*********************
//
RCP<Epetra_Map> Map;
RCP<Epetra_CrsMatrix> A;
RCP<Epetra_MultiVector> B, X;
RCP<Epetra_Vector> vecB, vecX;
EpetraExt::readEpetraLinearSystem(filename, Comm, &A, &Map, &vecX, &vecB);
A->OptimizeStorage();
proc_verbose = verbose && (MyPID==0); /* Only print on the zero processor */
// Check to see if the number of right-hand sides is the same as requested.
if (numrhs>1) {
X = rcp( new Epetra_MultiVector( *Map, numrhs ) );
B = rcp( new Epetra_MultiVector( *Map, numrhs ) );
X->Random();
OPT::Apply( *A, *X, *B );
X->PutScalar( 0.0 );
}
else {
X = Teuchos::rcp_implicit_cast<Epetra_MultiVector>(vecX);
B = Teuchos::rcp_implicit_cast<Epetra_MultiVector>(vecB);
}
// If requested, use a copy of B as initial guess
if (useRHSAsInitialGuess)
{
X->Update(1.0, *B, 0.0);
}
//
// ************Construct preconditioner*************
//
ParameterList ifpackList;
// allocates an IFPACK factory. No data is associated
// to this object (only method Create()).
Ifpack Factory;
// create the preconditioner. For valid PrecType values,
// please check the documentation
std::string PrecType = "ILU"; // incomplete LU
int OverlapLevel = 1; // must be >= 0. If Comm.NumProc() == 1,
// it is ignored.
RCP<Ifpack_Preconditioner> Prec = Teuchos::rcp( Factory.Create(PrecType, &*A, OverlapLevel) );
assert(Prec != Teuchos::null);
// specify parameters for ILU
ifpackList.set("fact: level-of-fill", 1);
// the combine mode is on the following:
// "Add", "Zero", "Insert", "InsertAdd", "Average", "AbsMax"
// Their meaning is as defined in file Epetra_CombineMode.h
ifpackList.set("schwarz: combine mode", "Add");
// sets the parameters
IFPACK_CHK_ERR(Prec->SetParameters(ifpackList));
// initialize the preconditioner. At this point the matrix must
// have been FillComplete()'d, but actual values are ignored.
IFPACK_CHK_ERR(Prec->Initialize());
// Builds the preconditioners, by looking for the values of
// the matrix.
IFPACK_CHK_ERR(Prec->Compute());
// Create the Belos preconditioned operator from the Ifpack preconditioner.
// NOTE: This is necessary because Belos expects an operator to apply the
// preconditioner with Apply() NOT ApplyInverse().
RCP<Belos::EpetraPrecOp> belosPrec = rcp( new Belos::EpetraPrecOp( Prec ) );
//
// *****Create parameter list for the block GMRES solver manager*****
//
const int NumGlobalElements = B->GlobalLength();
if (maxiters == -1)
maxiters = NumGlobalElements/blocksize - 1; // maximum number of iterations to run
//
ParameterList belosList;
belosList.set( "Flexible Gmres", true ); // Flexible Gmres will be used to solve this problem
belosList.set( "Num Blocks", maxsubspace ); // Maximum number of blocks in Krylov factorization
belosList.set( "Block Size", blocksize ); // Blocksize to be used by iterative solver
belosList.set( "Maximum Iterations", maxiters ); // Maximum number of iterations allowed
belosList.set( "Maximum Restarts", maxrestarts ); // Maximum number of restarts allowed
belosList.set( "Convergence Tolerance", tol ); // Relative convergence tolerance requested
if (numrhs > 1) {
belosList.set( "Show Maximum Residual Norm Only", true ); // Show only the maximum residual norm
}
if (verbose) {
belosList.set( "Verbosity", Belos::Errors + Belos::Warnings +
if (frequency > 0)
belosList.set( "Output Frequency", frequency );
}
else
belosList.set( "Verbosity", Belos::Errors + Belos::Warnings );
//
// *******Construct a preconditioned linear problem********
//
RCP<Belos::LinearProblem<double,MV,OP> > problem
problem->setRightPrec( belosPrec );
bool set = problem->setProblem();
if (set == false) {
if (proc_verbose)
std::cout << std::endl << "ERROR: Belos::LinearProblem failed to set up correctly!" << std::endl;
return EXIT_FAILURE;
}
// Create an iterative solver manager.
RCP< Belos::SolverManager<double,MV,OP> > solver
= rcp( new Belos::BlockGmresSolMgr<double,MV,OP>(problem, rcp(&belosList,false)));
//
// *******************************************************************
// *************Start the block Gmres iteration*************************
// *******************************************************************
//
if (proc_verbose) {
std::cout << std::endl << std::endl;
std::cout << "Dimension of matrix: " << NumGlobalElements << std::endl;
std::cout << "Number of right-hand sides: " << numrhs << std::endl;
std::cout << "Block size used by solver: " << blocksize << std::endl;
std::cout << "Number of restarts allowed: " << maxrestarts << std::endl;
std::cout << "Max number of Gmres iterations per restart cycle: " << maxiters << std::endl;
std::cout << "Relative residual tolerance: " << tol << std::endl;
std::cout << std::endl;
}
//
// Perform solve
//
Belos::ReturnType ret = solver->solve();
//
// Compute actual residuals.
//
bool badRes = false;
std::vector<double> actual_resids( numrhs );
std::vector<double> rhs_norm( numrhs );
Epetra_MultiVector resid(*Map, numrhs);
OPT::Apply( *A, *X, resid );
MVT::MvAddMv( -1.0, resid, 1.0, *B, resid );
MVT::MvNorm( resid, actual_resids );
MVT::MvNorm( *B, rhs_norm );
if (proc_verbose) {
std::cout<< "---------- Actual Residuals (normalized) ----------"<<std::endl<<std::endl;
for ( int i=0; i<numrhs; i++) {
double actRes = actual_resids[i]/rhs_norm[i];
std::cout<<"Problem "<<i<<" : \t"<< actRes <<std::endl;
if (actRes > tol) badRes = true;
}
}
success = ret==Belos::Converged && !badRes;
if (success) {
if (proc_verbose)
std::cout << "End Result: TEST PASSED" << std::endl;
} else {
if (proc_verbose)
std::cout << "End Result: TEST FAILED" << std::endl;
}
}
TEUCHOS_STANDARD_CATCH_STATEMENTS(verbose, std::cerr, success);
#ifdef EPETRA_MPI
MPI_Finalize();
#endif
return ( success ? EXIT_SUCCESS : EXIT_FAILURE );
}

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