static char help[] = "Tests incorrect use of MatDiagonalSet() for SHELL matrices\n\n";

#include <petscmat.h>

typedef struct _n_User *User;
struct _n_User {
  Mat B;
};

static PetscErrorCode MatGetDiagonal_User(Mat A, Vec X)
{
  User user;

  PetscFunctionBegin;
  PetscCall(MatShellGetContext(A, &user));
  PetscCall(MatGetDiagonal(user->B, X));
  PetscFunctionReturn(PETSC_SUCCESS);
}

int main(int argc, char **args)
{
  const PetscScalar xvals[] = {11, 13};
  const PetscInt    inds[]  = {0, 1};
  PetscScalar       avals[] = {2, 3, 5, 7};
  Mat               A, S;
  Vec               X, Y;
  User              user;

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &args, NULL, help));
  PetscCall(MatCreateSeqAIJ(PETSC_COMM_WORLD, 2, 2, 2, NULL, &A));
  PetscCall(MatSetUp(A));
  PetscCall(MatSetValues(A, 2, inds, 2, inds, avals, INSERT_VALUES));
  PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
  PetscCall(VecCreateSeq(PETSC_COMM_WORLD, 2, &X));
  PetscCall(VecSetValues(X, 2, inds, xvals, INSERT_VALUES));
  PetscCall(VecAssemblyBegin(X));
  PetscCall(VecAssemblyEnd(X));
  PetscCall(VecDuplicate(X, &Y));

  PetscCall(PetscNew(&user));
  user->B = A;

  PetscCall(MatCreateShell(PETSC_COMM_WORLD, 2, 2, 2, 2, user, &S));
  PetscCall(MatShellSetOperation(S, MATOP_GET_DIAGONAL, (PetscErrorCodeFn *)MatGetDiagonal_User));
  PetscCall(MatSetUp(S));

  PetscCall(MatShift(S, 42));
  PetscCall(MatGetDiagonal(S, Y));
  PetscCall(VecView(Y, PETSC_VIEWER_STDOUT_WORLD));
  PetscCall(MatDiagonalSet(S, X, ADD_VALUES));
  PetscCall(MatGetDiagonal(S, Y));
  PetscCall(VecView(Y, PETSC_VIEWER_STDOUT_WORLD));
  PetscCall(MatScale(S, 42));
  PetscCall(MatGetDiagonal(S, Y));
  PetscCall(VecView(Y, PETSC_VIEWER_STDOUT_WORLD));

  PetscCall(MatDestroy(&A));
  PetscCall(MatDestroy(&S));
  PetscCall(VecDestroy(&X));
  PetscCall(VecDestroy(&Y));
  PetscCall(PetscFree(user));
  PetscCall(PetscFinalize());
  return 0;
}

/*TEST

   test:
      args: -malloc_dump

TEST*/
