static char help[] = "Solve a matrix in parallel\n";

/*T
   Concepts: KSP^basic parallel example;
   Processors: n
T*/

/*
  Include "petscksp.h" so that we can use KSP solvers.  Note that this file
  automatically includes:
     petscsys.h       - base PETSc routines   petscvec.h - vectors
     petscmat.h - matrices
     petscis.h     - index sets            petscksp.h - Krylov subspace methods
     petscviewer.h - viewers               petscpc.h  - preconditioners

  Note:  The corresponding uniprocessor example is ex1.c
*/

#include <petsc.h>

#undef __FUNCT__
#define __FUNCT__ "main"
int main(int argc,char **args)
{
  Vec            x, b;          /* approx solution, RHS, exact solution */
  Mat            A, APre;                /* linear system matrix */
  KSP            ksp;              /* linear solver context */
  PetscErrorCode ierr;
  PetscViewer     fd;                     /* viewer */

  PetscInitialize(&argc,&args,(char*)0,help); 

  /*
     Load the matrix; then destroy the viewer.
  */
  ierr = PetscViewerBinaryOpen(PETSC_COMM_WORLD,"test_drdw.bin",FILE_MODE_READ,&fd);CHKERRQ(ierr);
  ierr = MatCreate(PETSC_COMM_WORLD,&A);CHKERRQ(ierr);
  ierr = MatSetFromOptions(A);CHKERRQ(ierr);
  ierr = MatLoad(A,fd);CHKERRQ(ierr);
  ierr = PetscViewerDestroy(&fd);CHKERRQ(ierr);
  /*
     Load the matrix; then destroy the viewer.
  */
  ierr = PetscViewerBinaryOpen(PETSC_COMM_WORLD,"test_drdwPre.bin",FILE_MODE_READ,&fd);CHKERRQ(ierr);
  ierr = MatCreate(PETSC_COMM_WORLD,&APre);CHKERRQ(ierr);
  ierr = MatSetFromOptions(APre);CHKERRQ(ierr);
  ierr = MatLoad(APre,fd);CHKERRQ(ierr);
  ierr = PetscViewerDestroy(&fd);CHKERRQ(ierr);
  ierr = MatCreateVecs(A, &x, &b);
  /*
     Set exact solution; then compute right-hand-side vector.
  */
  ierr = VecSet(b,1.0);CHKERRQ(ierr);
  ierr = KSPCreate(PETSC_COMM_WORLD,&ksp);CHKERRQ(ierr);
  ierr = KSPSetOperators(ksp,A,A);CHKERRQ(ierr);
  ierr = KSPSetFromOptions(ksp);CHKERRQ(ierr);
  printf("Solving...\n");
  ierr = KSPSolve(ksp,b,x);CHKERRQ(ierr);


  // Clean up
  ierr = VecDestroy(&x);CHKERRQ(ierr); 
  ierr = VecDestroy(&b);CHKERRQ(ierr); 
  ierr = MatDestroy(&A);CHKERRQ(ierr); 
  ierr = MatDestroy(&APre);CHKERRQ(ierr); 
  ierr = KSPDestroy(&ksp);CHKERRQ(ierr);

  /*
     Always call PetscFinalize() before exiting a program.  This routine
       - finalizes the PETSc libraries as well as MPI
       - provides summary and diagnostic information if certain runtime
         options are chosen (e.g., -log_summary).
  */
  ierr = PetscFinalize();
  return 0;
}