static char help[] = "Tests MatMeshToCellGraph()\n\n";

/*
  Include "petscmat.h" so that we can use matrices.
  automatically includes:
     petscsys.h       - base PETSc routines   petscvec.h    - vectors
     petscmat.h    - matrices
     petscis.h     - index sets            petscviewer.h - viewers
*/
#include <petscmat.h>

int main(int argc, char **args)
{
  Mat             mesh, dual;
  PetscInt        Nvertices = 6; /* total number of vertices */
  PetscInt        ncells    = 2; /* number cells on this process */
  PetscInt       *ii, *jj;
  PetscMPIInt     size, rank;
  MatPartitioning part;
  IS              is;

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &args, NULL, help));
  PetscCallMPI(MPI_Comm_size(MPI_COMM_WORLD, &size));
  PetscCheck(size == 2, PETSC_COMM_WORLD, PETSC_ERR_WRONG_MPI_SIZE, "This example is for exactly two processes");
  PetscCallMPI(MPI_Comm_rank(MPI_COMM_WORLD, &rank));

  PetscCall(PetscMalloc1(3, &ii));
  PetscCall(PetscMalloc1(6, &jj));
  ii[0] = 0;
  ii[1] = 3;
  ii[2] = 6;
  if (rank == 0) {
    jj[0] = 0;
    jj[1] = 1;
    jj[2] = 2;
    jj[3] = 1;
    jj[4] = 2;
    jj[5] = 3;
  } else {
    jj[0] = 1;
    jj[1] = 4;
    jj[2] = 5;
    jj[3] = 1;
    jj[4] = 3;
    jj[5] = 5;
  }
  PetscCall(MatCreateMPIAdj(MPI_COMM_WORLD, ncells, Nvertices, ii, jj, NULL, &mesh));
  PetscCall(MatMeshToCellGraph(mesh, 2, &dual));
  PetscCall(MatView(dual, PETSC_VIEWER_STDOUT_WORLD));

  PetscCall(MatPartitioningCreate(MPI_COMM_WORLD, &part));
  PetscCall(MatPartitioningSetAdjacency(part, dual));
  PetscCall(MatPartitioningSetFromOptions(part));
  PetscCall(MatPartitioningApply(part, &is));
  PetscCall(ISView(is, PETSC_VIEWER_STDOUT_WORLD));
  PetscCall(ISDestroy(&is));
  PetscCall(MatPartitioningDestroy(&part));

  PetscCall(MatDestroy(&mesh));
  PetscCall(MatDestroy(&dual));
  PetscCall(PetscFinalize());
  return 0;
}

/*TEST

   build:
     requires: parmetis

   test:
      nsize: 2

TEST*/