```// @HEADER
// ***********************************************************************
//
//
// Under terms of Contract DE-AC04-94AL85000, there is a non-exclusive
// license for use of this work by or on behalf of the U.S. Government.
//
// 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
//
// 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
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//
// ***********************************************************************

// Solve a linear system with AztecOO.
// The linear system is created using MatrixGallery

#include "Epetra_ConfigDefs.h"
#ifdef HAVE_MPI
#include "mpi.h"
#include "Epetra_MpiComm.h"
#else
#include "Epetra_SerialComm.h"
#endif
#include "AztecOO.h"
#include "Epetra_CrsMatrix.h"

#include "Trilinos_Util_CrsMatrixGallery.h"

using namespace Trilinos_Util;

int main(int argc, char *argv[])
{

#ifdef HAVE_MPI
MPI_Init(&argc,&argv);
Epetra_MpiComm Comm(MPI_COMM_WORLD);
#else
Epetra_SerialComm Comm;
#endif

// initialize an Gallery object
CrsMatrixGallery Gallery("laplace_2d", Comm);
Gallery.Set("problem_size",900);

// Get pointers to the linear problem (containing matrix, LHS and RHS).
Epetra_LinearProblem * Problem= Gallery.GetLinearProblem();

// initialize the AztecOO solve object, based on current linear problem
AztecOO solver(*Problem);

// here set some AztecOO options:
// - symmetric problem;
// - domain decomposition preconditioner
// - ICC factorization on each subdomain
solver.SetAztecOption(AZ_solver, AZ_cg_condnum);
solver.SetAztecOption(AZ_precond, AZ_dom_decomp);
solver.SetAztecOption(AZ_overlap,0);
solver.SetAztecOption(AZ_subdomain_solve, AZ_icc);

// solve the linear system
solver.Iterate(1550, 1e-12);

// AztecOO defined a certain number of output parameters, and store them
// in a double vector called status.
double status[AZ_STATUS_SIZE];
solver.GetAllAztecStatus(status);

// verify that linear system has been solved as required
double residual, diff;

Gallery.ComputeResidual(&residual);
Gallery.ComputeDiffBetweenStartingAndExactSolutions(&diff);

if( Comm.MyPID()==0 ) {
cout << "||b-Ax||_2 = " << residual << endl;
cout << "||x_exact - x||_2 = " << diff << endl;
}

#ifdef HAVE_MPI
MPI_Finalize();
#endif

return(EXIT_SUCCESS);

}

#else

#include <stdlib.h>
#include <stdio.h>
#ifdef HAVE_MPI
#include "mpi.h"
#endif

int main(int argc, char *argv[])
{
#ifdef HAVE_MPI
MPI_Init(&argc,&argv);
#endif

"--enable-epetra\n"
"--enable-triutils\n"
"--enable-aztecoo\n");

#ifdef HAVE_MPI
MPI_Finalize();
#endif
return 0;
}

#endif

```