static char help[] = "Tests MatMult() after MatDuplicate().\n\n";

#include <petscmat.h>

int main(int argc,char **args)
{
  Mat            A,B;
  Vec            x,y;
  PetscErrorCode ierr;
  PetscInt       i,j,m=10,n,rstart,rend;
  PetscScalar    v;
  PetscBool      diag=PETSC_FALSE;

  ierr = PetscInitialize(&argc,&args,(char*)0,help);if (ierr) return ierr;
  ierr = PetscOptionsGetInt(NULL,NULL,"-m",&m,NULL);CHKERRQ(ierr);
  n    = m;
  ierr = PetscOptionsHasName(NULL,NULL,"-diag",&diag);CHKERRQ(ierr);

  /* ---------- Assemble matrix and vectors ----------- */

  ierr = MatCreate(PETSC_COMM_WORLD,&A);CHKERRQ(ierr);
  ierr = MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,m,n);CHKERRQ(ierr);
  ierr = MatSetFromOptions(A);CHKERRQ(ierr);
  ierr = MatSetUp(A);CHKERRQ(ierr);
  ierr = MatGetOwnershipRange(A,&rstart,&rend);CHKERRQ(ierr);
  ierr = VecCreate(PETSC_COMM_WORLD,&x);CHKERRQ(ierr);
  ierr = VecSetSizes(x,PETSC_DECIDE,m);CHKERRQ(ierr);
  ierr = VecSetFromOptions(x);CHKERRQ(ierr);
  ierr = VecCreate(PETSC_COMM_WORLD,&y);CHKERRQ(ierr);
  ierr = VecSetSizes(y,PETSC_DECIDE,n);CHKERRQ(ierr);
  ierr = VecSetFromOptions(y);CHKERRQ(ierr);

  ierr = VecSet(x,1.0);CHKERRQ(ierr);
  ierr = VecSet(y,0.0);CHKERRQ(ierr);

  for (i=rstart; i<rend; i++) {
    for (j=0; j<n; j++) {
      v    = 10*(i+1)+j+1;
      if (i == j) {
          ierr = MatSetValues(A,1,&i,1,&j,&v,INSERT_VALUES);CHKERRQ(ierr);
      }
      if (i != j && !diag) {
          ierr = MatSetValues(A,1,&i,1,&j,&v,INSERT_VALUES);CHKERRQ(ierr);
      }
    }
  }

  ierr = MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
  ierr = MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);

  /* Duplicate the matrix */
  ierr = MatDuplicate(A,MAT_COPY_VALUES,&B);CHKERRQ(ierr);
  ierr = MatView(A,0);CHKERRQ(ierr);

  /* ------------ Test MatMult() ---------- */

  ierr = PetscPrintf(PETSC_COMM_WORLD,"testing MatMult()\n");CHKERRQ(ierr);
  ierr = MatMult(B,x,y);CHKERRQ(ierr);
  /* print something */
  ierr = VecView(y,0);CHKERRQ(ierr);

  /* Free data structures */
  ierr = VecDestroy(&x);CHKERRQ(ierr);
  ierr = VecDestroy(&y);CHKERRQ(ierr);
  ierr = MatDestroy(&A);CHKERRQ(ierr);
  ierr = MatDestroy(&B);CHKERRQ(ierr);

  ierr = PetscFinalize();
  return ierr;
}