static char help[] = "Tests MatOption MAT_FORCE_DIAGONAL_ENTRIES.\n\n";

#include <petscmat.h>

int main(int argc,char **args)
{
  Mat            A,B;
  Vec            diag;
  PetscInt       i,n = 10,col[3],test;
  PetscScalar    v[3];

  PetscCall(PetscInitialize(&argc,&args,(char*)0,help));
  PetscCall(PetscOptionsGetInt(NULL,NULL,"-n",&n,NULL));

  /* Create A which has empty 0-th row and column */
  PetscCall(MatCreate(PETSC_COMM_WORLD,&A));
  PetscCall(MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,n,n));
  PetscCall(MatSetType(A,MATAIJ));
  PetscCall(MatSetFromOptions(A));
  PetscCall(MatSetUp(A));

  v[0] = -1.; v[1] = 2.; v[2] = -1.;
  for (i=2; i<n-1; i++) {
    col[0] = i-1; col[1] = i; col[2] = i+1;
    PetscCall(MatSetValues(A,1,&i,3,col,v,INSERT_VALUES));
  }
  i    = 1; col[0] = 1; col[1] = 2;
  PetscCall(MatSetValues(A,1,&i,2,col,v+1,INSERT_VALUES));
  i    = n - 1; col[0] = n - 2; col[1] = n - 1;
  PetscCall(MatSetValues(A,1,&i,2,col,v,INSERT_VALUES));
  PetscCall(MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY));

  for (test = 0; test < 2; test++) {
    PetscCall(MatProductCreate(A,A,NULL,&B));

    if (test == 0) {
      /* Compute B = A*A; B misses 0-th diagonal */
      PetscCall(MatProductSetType(B,MATPRODUCT_AB));
      PetscCall(MatSetOptionsPrefix(B,"AB_"));
    } else {
      /* Compute B = A^t*A; B misses 0-th diagonal */
      PetscCall(MatProductSetType(B,MATPRODUCT_AtB));
      PetscCall(MatSetOptionsPrefix(B,"AtB_"));
    }

    /* Force allocate missing diagonal entries of B */
    PetscCall(MatSetOption(B,MAT_FORCE_DIAGONAL_ENTRIES,PETSC_TRUE));
    PetscCall(MatProductSetFromOptions(B));

    PetscCall(MatProductSymbolic(B));
    PetscCall(MatProductNumeric(B));

    PetscCall(MatSetOption(B,MAT_NEW_NONZERO_LOCATION_ERR,PETSC_TRUE));

    /* Insert entries to diagonal of B */
    PetscCall(MatCreateVecs(B,NULL,&diag));
    PetscCall(MatGetDiagonal(B,diag));
    PetscCall(VecSetValue(diag,0,100.0,INSERT_VALUES));
    PetscCall(VecAssemblyBegin(diag));
    PetscCall(VecAssemblyEnd(diag));

    PetscCall(MatDiagonalSet(B,diag,INSERT_VALUES));
    if (test == 1) {
      PetscCall(MatView(B,PETSC_VIEWER_STDOUT_WORLD));
    }
    PetscCall(MatDestroy(&B));
    PetscCall(VecDestroy(&diag));
  }

  PetscCall(MatDestroy(&A));
  PetscCall(PetscFinalize());
  return 0;
}

/*TEST

   test:
     output_file: output/ex81_1.out

   test:
     suffix: 2
     args: -AtB_mat_product_algorithm at*b
     output_file: output/ex81_1.out

   test:
     suffix: 3
     args: -AtB_mat_product_algorithm outerproduct
     output_file: output/ex81_1.out

   test:
     suffix: 4
     nsize: 3
     args: -AtB_mat_product_algorithm nonscalable
     output_file: output/ex81_3.out

   test:
     suffix: 5
     nsize: 3
     args: -AtB_mat_product_algorithm scalable
     output_file: output/ex81_3.out

   test:
     suffix: 6
     nsize: 3
     args: -AtB_mat_product_algorithm at*b
     output_file: output/ex81_3.out

TEST*/