static const char help[] = "Tests MatGetSchurComplement\n";

#include <petscksp.h>

PetscErrorCode Create(MPI_Comm comm, Mat *inA, IS *is0, IS *is1)
{
  Mat         A;
  PetscInt    r, rend, M;
  PetscMPIInt rank;

  PetscFunctionBeginUser;
  *inA = 0;
  PetscCall(MatCreate(comm, &A));
  PetscCall(MatSetSizes(A, 4, 4, PETSC_DETERMINE, PETSC_DETERMINE));
  PetscCall(MatSetFromOptions(A));
  PetscCall(MatSetUp(A));
  PetscCall(MatGetOwnershipRange(A, &r, &rend));
  PetscCall(MatGetSize(A, &M, NULL));

  PetscCall(ISCreateStride(comm, 2, r, 1, is0));
  PetscCall(ISCreateStride(comm, 2, r + 2, 1, is1));

  PetscCallMPI(MPI_Comm_rank(comm, &rank));

  {
    PetscInt    rows[4], cols0[5], cols1[5], cols2[3], cols3[3];
    PetscScalar RR = 1000. * rank, vals0[5], vals1[4], vals2[3], vals3[3];

    rows[0] = r;
    rows[1] = r + 1;
    rows[2] = r + 2;
    rows[3] = r + 3;

    cols0[0] = r + 0;
    cols0[1] = r + 1;
    cols0[2] = r + 3;
    cols0[3] = (r + 4) % M;
    cols0[4] = (r + M - 4) % M;

    cols1[0] = r + 1;
    cols1[1] = r + 2;
    cols1[2] = (r + 4 + 1) % M;
    cols1[3] = (r + M - 4 + 1) % M;

    cols2[0] = r;
    cols2[1] = r + 2;
    cols2[2] = (r + 4 + 2) % M;

    cols3[0] = r + 1;
    cols3[1] = r + 3;
    cols3[2] = (r + 4 + 3) % M;

    vals0[0] = RR + 1.;
    vals0[1] = RR + 2.;
    vals0[2] = RR + 3.;
    vals0[3] = RR + 4.;
    vals0[4] = RR + 5.;

    vals1[0] = RR + 6.;
    vals1[1] = RR + 7.;
    vals1[2] = RR + 8.;
    vals1[3] = RR + 9.;

    vals2[0] = RR + 10.;
    vals2[1] = RR + 11.;
    vals2[2] = RR + 12.;

    vals3[0] = RR + 13.;
    vals3[1] = RR + 14.;
    vals3[2] = RR + 15.;
    PetscCall(MatSetValues(A, 1, &rows[0], 5, cols0, vals0, INSERT_VALUES));
    PetscCall(MatSetValues(A, 1, &rows[1], 4, cols1, vals1, INSERT_VALUES));
    PetscCall(MatSetValues(A, 1, &rows[2], 3, cols2, vals2, INSERT_VALUES));
    PetscCall(MatSetValues(A, 1, &rows[3], 3, cols3, vals3, INSERT_VALUES));
  }
  PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
  *inA = A;
  PetscFunctionReturn(PETSC_SUCCESS);
}

PetscErrorCode Destroy(Mat *A, IS *is0, IS *is1)
{
  PetscFunctionBeginUser;
  PetscCall(MatDestroy(A));
  PetscCall(ISDestroy(is0));
  PetscCall(ISDestroy(is1));
  PetscFunctionReturn(PETSC_SUCCESS);
}

int main(int argc, char *argv[])
{
  Mat                        A, S = NULL, Sexplicit = NULL, Sp, B, C;
  MatSchurComplementAinvType ainv_type = MAT_SCHUR_COMPLEMENT_AINV_DIAG;
  IS                         is0, is1;
  PetscBool                  flg;
  PetscInt                   m, N = 10;

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &argv, 0, help));
  PetscOptionsBegin(PETSC_COMM_WORLD, NULL, "ex21", "KSP");
  PetscCall(PetscOptionsEnum("-mat_schur_complement_ainv_type", "Type of approximation for inv(A00) used when assembling Sp = A11 - A10 inv(A00) A01", "MatSchurComplementAinvType", MatSchurComplementAinvTypes, (PetscEnum)ainv_type, (PetscEnum *)&ainv_type, NULL));
  PetscOptionsEnd();

  /* Test the Schur complement one way */
  PetscCall(Create(PETSC_COMM_WORLD, &A, &is0, &is1));
  PetscCall(MatView(A, PETSC_VIEWER_STDOUT_WORLD));
  PetscCall(ISView(is0, PETSC_VIEWER_STDOUT_WORLD));
  PetscCall(ISView(is1, PETSC_VIEWER_STDOUT_WORLD));
  PetscCall(MatGetSchurComplement(A, is0, is0, is1, is1, MAT_INITIAL_MATRIX, &S, ainv_type, MAT_IGNORE_MATRIX, NULL));
  PetscCall(MatSetFromOptions(S));
  PetscCall(MatComputeOperator(S, MATAIJ, &Sexplicit));
  PetscCall(PetscPrintf(PETSC_COMM_WORLD, "\nExplicit Schur complement of (0,0) in (1,1)\n"));
  PetscCall(MatView(Sexplicit, PETSC_VIEWER_STDOUT_WORLD));
  if (ainv_type == MAT_SCHUR_COMPLEMENT_AINV_DIAG) {
    PetscCall(MatSchurComplementSetAinvType(S, MAT_SCHUR_COMPLEMENT_AINV_FULL));
    PetscCall(MatSchurComplementGetPmat(S, MAT_INITIAL_MATRIX, &Sp));
    PetscCall(MatMultEqual(Sp, Sexplicit, 10, &flg));
    PetscCheck(flg, PETSC_COMM_WORLD, PETSC_ERR_PLIB, "Sp != S");
    PetscCall(MatSchurComplementSetAinvType(S, MAT_SCHUR_COMPLEMENT_AINV_DIAG));
    PetscCall(MatDestroy(&Sp));
  }
  PetscCall(Destroy(&A, &is0, &is1));
  if (ainv_type == MAT_SCHUR_COMPLEMENT_AINV_DIAG) {
    PetscCall(MatGetLocalSize(Sexplicit, &m, NULL));
    PetscCall(MatCreateDense(PetscObjectComm((PetscObject)Sexplicit), m, PETSC_DECIDE, PETSC_DECIDE, N, NULL, &B));
    PetscCall(MatSetRandom(B, NULL));
    PetscCall(MatMatMult(S, B, MAT_INITIAL_MATRIX, PETSC_DETERMINE, &C));
    PetscCall(MatMatMultEqual(Sexplicit, B, C, 10, &flg));
    PetscCheck(flg, PETSC_COMM_WORLD, PETSC_ERR_PLIB, "S*B != C");
    PetscCall(MatDestroy(&C));
    PetscCall(MatDestroy(&B));
  }
  PetscCall(MatDestroy(&S));
  PetscCall(MatDestroy(&Sexplicit));

  /* And the other */
  PetscCall(Create(PETSC_COMM_WORLD, &A, &is0, &is1));
  PetscCall(MatGetSchurComplement(A, is1, is1, is0, is0, MAT_INITIAL_MATRIX, &S, ainv_type, MAT_IGNORE_MATRIX, NULL));
  PetscCall(MatSetFromOptions(S));
  PetscCall(MatComputeOperator(S, MATAIJ, &Sexplicit));
  PetscCall(PetscPrintf(PETSC_COMM_WORLD, "\nExplicit Schur complement of (1,1) in (0,0)\n"));
  PetscCall(MatView(Sexplicit, PETSC_VIEWER_STDOUT_WORLD));
  if (ainv_type == MAT_SCHUR_COMPLEMENT_AINV_DIAG) {
    PetscCall(MatSchurComplementSetAinvType(S, MAT_SCHUR_COMPLEMENT_AINV_FULL));
    PetscCall(MatSchurComplementGetPmat(S, MAT_INITIAL_MATRIX, &Sp));
    PetscCall(MatMultEqual(Sp, Sexplicit, 10, &flg));
    PetscCheck(flg, PETSC_COMM_WORLD, PETSC_ERR_PLIB, "Sp != S");
    PetscCall(MatSchurComplementSetAinvType(S, MAT_SCHUR_COMPLEMENT_AINV_DIAG));
    PetscCall(MatDestroy(&Sp));
  }
  PetscCall(Destroy(&A, &is0, &is1));
  if (ainv_type == MAT_SCHUR_COMPLEMENT_AINV_DIAG) {
    PetscCall(MatGetLocalSize(Sexplicit, &m, NULL));
    PetscCall(MatCreateDense(PetscObjectComm((PetscObject)Sexplicit), m, PETSC_DECIDE, PETSC_DECIDE, N, NULL, &B));
    PetscCall(MatSetRandom(B, NULL));
    PetscCall(MatMatMult(S, B, MAT_INITIAL_MATRIX, PETSC_DETERMINE, &C));
    PetscCall(MatMatMultEqual(Sexplicit, B, C, 10, &flg));
    PetscCheck(flg, PETSC_COMM_WORLD, PETSC_ERR_PLIB, "S*B != C");
    PetscCall(MatDestroy(&C));
    PetscCall(MatDestroy(&B));
  }
  PetscCall(MatDestroy(&S));
  PetscCall(MatDestroy(&Sexplicit));

  /* This time just the preconditioning matrix. */
  PetscCall(Create(PETSC_COMM_WORLD, &A, &is0, &is1));
  PetscCall(MatGetSchurComplement(A, is0, is0, is1, is1, MAT_IGNORE_MATRIX, NULL, ainv_type, MAT_INITIAL_MATRIX, &S));
  PetscCall(MatSetFromOptions(S));
  PetscCall(PetscPrintf(PETSC_COMM_WORLD, "\nPreconditioning Schur complement of (0,0) in (1,1)\n"));
  PetscCall(MatView(S, PETSC_VIEWER_STDOUT_WORLD));
  /* Modify and refresh */
  PetscCall(MatShift(A, 1.));
  PetscCall(MatGetSchurComplement(A, is0, is0, is1, is1, MAT_IGNORE_MATRIX, NULL, ainv_type, MAT_REUSE_MATRIX, &S));
  PetscCall(PetscPrintf(PETSC_COMM_WORLD, "\nAfter update\n"));
  PetscCall(MatView(S, PETSC_VIEWER_STDOUT_WORLD));
  PetscCall(Destroy(&A, &is0, &is1));
  PetscCall(MatDestroy(&S));

  PetscCall(PetscFinalize());
  return 0;
}

/*TEST
  test:
    suffix: diag_1
    args: -mat_schur_complement_ainv_type diag
    nsize: 1
  test:
    suffix: blockdiag_1
    args: -mat_schur_complement_ainv_type blockdiag
    nsize: 1
  test:
    suffix: diag_2
    args: -mat_schur_complement_ainv_type diag
    nsize: 2
  test:
    suffix: blockdiag_2
    args: -mat_schur_complement_ainv_type blockdiag
    nsize: 2
  test:
    # does not work with single because residual norm computed by GMRES recurrence formula becomes invalid
    requires: !single
    suffix: diag_3
    args: -mat_schur_complement_ainv_type diag -ksp_rtol 1e-12
    nsize: 3
  test:
    # does not work with single because residual norm computed by GMRES recurrence formula becomes invalid
    requires: !single
    suffix: blockdiag_3
    args: -mat_schur_complement_ainv_type blockdiag
    nsize: 3
TEST*/
