static char help[] = "Test MatTransposeMatMult() \n\n";

/* Example:
  mpiexec -n 8 ./ex209 -f <inputfile> (e.g., inputfile=ceres_solver_iteration_001_A.petsc)
*/

#include <petscmat.h>

int main(int argc, char **args)
{
  Mat         A, C, AtA, B;
  PetscViewer fd;
  char        file[PETSC_MAX_PATH_LEN];
  PetscReal   fill = 4.0;
  PetscMPIInt rank, size;
  PetscBool   equal;
  PetscInt    i, m, n, rstart, rend;
  PetscScalar one = 1.0;

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &args, NULL, help));
  PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));
  PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
  PetscCall(PetscOptionsGetString(NULL, NULL, "-f", file, sizeof(file), NULL));

  /* Load matrix A */
  PetscCall(PetscViewerBinaryOpen(PETSC_COMM_WORLD, file, FILE_MODE_READ, &fd));
  PetscCall(MatCreate(PETSC_COMM_WORLD, &A));
  PetscCall(MatSetType(A, MATAIJ));
  PetscCall(MatLoad(A, fd));
  PetscCall(PetscViewerDestroy(&fd));

  /* Create identity matrix B */
  PetscCall(MatGetLocalSize(A, &m, &n));
  PetscCall(MatCreate(PETSC_COMM_WORLD, &B));
  PetscCall(MatSetSizes(B, m, m, PETSC_DECIDE, PETSC_DECIDE));
  PetscCall(MatSetType(B, MATAIJ));
  PetscCall(MatSetFromOptions(B));
  PetscCall(MatSetUp(B));

  PetscCall(MatGetOwnershipRange(B, &rstart, &rend));
  for (i = rstart; i < rend; i++) PetscCall(MatSetValues(B, 1, &i, 1, &i, &one, INSERT_VALUES));
  PetscCall(MatAssemblyBegin(B, MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(B, MAT_FINAL_ASSEMBLY));

  /* Compute AtA = A^T*B*A, B = identity matrix */
  PetscCall(MatPtAP(B, A, MAT_INITIAL_MATRIX, fill, &AtA));
  PetscCall(MatPtAP(B, A, MAT_REUSE_MATRIX, fill, &AtA));
  if (rank == 0) printf("C = A^T*B*A is done...\n");
  PetscCall(MatDestroy(&B));

  /* Compute C = A^T*A */
  PetscCall(MatTransposeMatMult(A, A, MAT_INITIAL_MATRIX, fill, &C));
  if (rank == 0) printf("C = A^T*A is done...\n");
  PetscCall(MatTransposeMatMult(A, A, MAT_REUSE_MATRIX, fill, &C));
  if (rank == 0) printf("REUSE C = A^T*A is done...\n");

  /* Compare C and AtA */
  PetscCall(MatMultEqual(C, AtA, 20, &equal));
  PetscCheck(equal, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "A^T*A != At*A");
  PetscCall(MatDestroy(&AtA));

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

/*TEST

   test:
      requires: datafilespath !complex double !defined(PETSC_USE_64BIT_INDICES)
      args: -f ${DATAFILESPATH}/matrices/arco1

   test:
      suffix: 2
      nsize: 4
      requires: datafilespath !complex double !defined(PETSC_USE_64BIT_INDICES)
      args: -f ${DATAFILESPATH}/matrices/arco1 -matptap_via nonscalable

TEST*/