static char help[] = "Testing PtAP for SeqMAIJ matrix, P, with SeqAIJ matrix, A.\n\n";

#include <petscmat.h>

int main(int argc, char **argv)
{
  Mat         pA, P, aijP;
  PetscScalar pa[] = {1., -1., 0., 0., 1., -1., 0., 0., 1.};
  PetscInt    i, pij[] = {0, 1, 2};
  PetscInt    aij[3][3] = {
    {0, 1, 2},
    {3, 4, 5},
    {6, 7, 8}
  };
  Mat                 A, mC, C;
  PetscScalar         one = 1.;
  PetscMPIInt         size;
  PetscBool           flg;
  MatProductAlgorithm alg;

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &argv, NULL, help));
  PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
  PetscCheck(size == 1, PETSC_COMM_WORLD, PETSC_ERR_WRONG_MPI_SIZE, "This is a uniprocessor example only!");

  /* Create MAIJ matrix, P */
  PetscCall(MatCreate(PETSC_COMM_SELF, &pA));
  PetscCall(MatSetSizes(pA, 3, 3, 3, 3));
  PetscCall(MatSetType(pA, MATSEQAIJ));
  PetscCall(MatSetUp(pA));
  PetscCall(MatSetOption(pA, MAT_IGNORE_ZERO_ENTRIES, PETSC_TRUE));
  PetscCall(MatSetValues(pA, 3, pij, 3, pij, pa, ADD_VALUES));
  PetscCall(MatAssemblyBegin(pA, MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(pA, MAT_FINAL_ASSEMBLY));
  PetscCall(MatCreateMAIJ(pA, 3, &P));
  PetscCall(MatDestroy(&pA));

  /* Create AIJ equivalent matrix, aijP, for comparison testing */
  PetscCall(MatConvert(P, MATSEQAIJ, MAT_INITIAL_MATRIX, &aijP));

  /* Create AIJ matrix A */
  PetscCall(MatCreate(PETSC_COMM_SELF, &A));
  PetscCall(MatSetSizes(A, 9, 9, 9, 9));
  PetscCall(MatSetType(A, MATSEQAIJ));
  PetscCall(MatSetUp(A));
  PetscCall(MatSetOption(A, MAT_IGNORE_ZERO_ENTRIES, PETSC_TRUE));
  PetscCall(MatSetValues(A, 3, aij[0], 3, aij[0], pa, ADD_VALUES));
  PetscCall(MatSetValues(A, 3, aij[1], 3, aij[1], pa, ADD_VALUES));
  PetscCall(MatSetValues(A, 3, aij[2], 3, aij[2], pa, ADD_VALUES));
  for (i = 0; i < 9; i++) PetscCall(MatSetValue(A, i, i, one, ADD_VALUES));
  PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));

  /* Perform PtAP_SeqAIJ_SeqAIJ for comparison testing */
  PetscCall(MatPtAP(A, aijP, MAT_INITIAL_MATRIX, 1., &C));

  /* Perform PtAP_SeqAIJ_SeqMAIJ */
  /* Developer API */
  PetscCall(MatProductCreate(A, P, NULL, &mC));
  PetscCall(MatProductSetType(mC, MATPRODUCT_PtAP));
  PetscCall(MatProductSetAlgorithm(mC, MATPRODUCTALGORITHMDEFAULT));
  PetscCall(MatProductSetFill(mC, PETSC_DEFAULT));
  PetscCall(MatProductSetFromOptions(mC));
  PetscCall(MatProductSymbolic(mC));
  PetscCall(MatProductNumeric(mC));
  PetscCall(MatProductNumeric(mC));
  PetscCall(MatProductGetAlgorithm(mC, &alg));
  PetscCall(PetscPrintf(PETSC_COMM_SELF, "MatProduct algorithm: %s\n", alg));

  /* Check mC = C */
  PetscCall(MatEqual(C, mC, &flg));
  PetscCheck(flg, PETSC_COMM_SELF, PETSC_ERR_ARG_INCOMP, "MatProduct C != mC");
  PetscCall(MatDestroy(&mC));

  /* User API */
  PetscCall(MatPtAP(A, P, MAT_INITIAL_MATRIX, 1., &mC));
  PetscCall(MatPtAP(A, P, MAT_REUSE_MATRIX, 1., &mC));

  /* Check mC = C */
  PetscCall(MatEqual(C, mC, &flg));
  PetscCheck(flg, PETSC_COMM_SELF, PETSC_ERR_ARG_INCOMP, "MatPtAP C != mC");
  PetscCall(MatDestroy(&mC));

  /* Cleanup */
  PetscCall(MatDestroy(&P));
  PetscCall(MatDestroy(&aijP));
  PetscCall(MatDestroy(&A));
  PetscCall(MatDestroy(&C));
  PetscCall(PetscFinalize());
  return 0;
}

/*TEST

   test:
      output_file: output/ex101.out

TEST*/