static char help[] = "Tests DMCreateDomainDecomposition.\n\n";

/*
Use the options
     -da_grid_x <nx> - number of grid points in x direction, if M < 0
     -da_grid_y <ny> - number of grid points in y direction, if N < 0
     -da_processors_x <MX> number of processors in x directio
     -da_processors_y <MY> number of processors in x direction
*/

#include <petscdm.h>
#include <petscdmda.h>

PetscErrorCode FillLocalSubdomain(DM da, Vec gvec)
{
  DMDALocalInfo info;
  PetscMPIInt   rank;
  PetscInt      i, j, k, l;

  PetscFunctionBeginUser;
  PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));
  PetscCall(DMDAGetLocalInfo(da, &info));

  if (info.dim == 3) {
    PetscScalar ***g;
    PetscCall(DMDAVecGetArray(da, gvec, &g));
    /* loop over ghosts */
    for (k = info.zs; k < info.zs + info.zm; k++) {
      for (j = info.ys; j < info.ys + info.ym; j++) {
        for (i = info.xs; i < info.xs + info.xm; i++) {
          g[k][j][info.dof * i + 0] = i;
          g[k][j][info.dof * i + 1] = j;
          g[k][j][info.dof * i + 2] = k;
        }
      }
    }
    PetscCall(DMDAVecRestoreArray(da, gvec, &g));
  }
  if (info.dim == 2) {
    PetscScalar **g;
    PetscCall(DMDAVecGetArray(da, gvec, &g));
    /* loop over ghosts */
    for (j = info.ys; j < info.ys + info.ym; j++) {
      for (i = info.xs; i < info.xs + info.xm; i++) {
        for (l = 0; l < info.dof; l++) {
          g[j][info.dof * i + 0] = i;
          g[j][info.dof * i + 1] = j;
          g[j][info.dof * i + 2] = rank;
        }
      }
    }
    PetscCall(DMDAVecRestoreArray(da, gvec, &g));
  }
  PetscFunctionReturn(PETSC_SUCCESS);
}

int main(int argc, char **argv)
{
  DM            da, *subda;
  PetscInt      i, dim = 3;
  PetscInt      M = 25, N = 25, P = 25;
  PetscMPIInt   size, rank;
  Vec           v;
  Vec           slvec, sgvec;
  IS           *ois, *iis;
  VecScatter    oscata;
  VecScatter   *iscat, *oscat, *gscat;
  DMDALocalInfo info;
  PetscBool     patchis_offproc = PETSC_TRUE;

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &argv, (char *)0, help));
  PetscCall(PetscOptionsGetInt(NULL, NULL, "-dim", &dim, NULL));

  /* Create distributed array and get vectors */
  PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
  PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));
  if (dim == 2) {
    PetscCall(DMDACreate2d(PETSC_COMM_WORLD, DM_BOUNDARY_NONE, DM_BOUNDARY_NONE, DMDA_STENCIL_STAR, M, N, PETSC_DECIDE, PETSC_DECIDE, 3, 1, NULL, NULL, &da));
  } else if (dim == 3) {
    PetscCall(DMDACreate3d(PETSC_COMM_WORLD, DM_BOUNDARY_NONE, DM_BOUNDARY_NONE, DM_BOUNDARY_NONE, DMDA_STENCIL_STAR, M, N, P, PETSC_DECIDE, PETSC_DECIDE, PETSC_DECIDE, 3, 1, NULL, NULL, NULL, &da));
  }
  PetscCall(DMSetFromOptions(da));
  PetscCall(DMSetUp(da));
  PetscCall(DMDAGetLocalInfo(da, &info));

  PetscCall(DMCreateDomainDecomposition(da, NULL, NULL, &iis, &ois, &subda));
  PetscCall(DMCreateDomainDecompositionScatters(da, 1, subda, &iscat, &oscat, &gscat));

  {
    DMDALocalInfo subinfo;
    MatStencil    lower, upper;
    IS            patchis;
    Vec           smallvec;
    Vec           largevec;
    VecScatter    patchscat;

    PetscCall(DMDAGetLocalInfo(subda[0], &subinfo));

    lower.i = info.xs;
    lower.j = info.ys;
    lower.k = info.zs;
    upper.i = info.xs + info.xm;
    upper.j = info.ys + info.ym;
    upper.k = info.zs + info.zm;

    /* test the patch IS as a thing to scatter to/from */
    PetscCall(DMDACreatePatchIS(da, &lower, &upper, &patchis, patchis_offproc));
    PetscCall(DMGetGlobalVector(da, &largevec));

    PetscCall(VecCreate(PETSC_COMM_SELF, &smallvec));
    PetscCall(VecSetSizes(smallvec, info.dof * (upper.i - lower.i) * (upper.j - lower.j) * (upper.k - lower.k), PETSC_DECIDE));
    PetscCall(VecSetFromOptions(smallvec));
    PetscCall(VecScatterCreate(smallvec, NULL, largevec, patchis, &patchscat));

    PetscCall(FillLocalSubdomain(subda[0], smallvec));
    PetscCall(VecSet(largevec, 0));

    PetscCall(VecScatterBegin(patchscat, smallvec, largevec, ADD_VALUES, SCATTER_FORWARD));
    PetscCall(VecScatterEnd(patchscat, smallvec, largevec, ADD_VALUES, SCATTER_FORWARD));
    PetscCall(ISView(patchis, PETSC_VIEWER_STDOUT_WORLD));
    PetscCall(VecScatterView(patchscat, PETSC_VIEWER_STDOUT_WORLD));

    for (i = 0; i < size; i++) {
      if (i == rank) PetscCall(VecView(smallvec, PETSC_VIEWER_STDOUT_SELF));
      PetscCallMPI(MPI_Barrier(PETSC_COMM_WORLD));
    }

    PetscCallMPI(MPI_Barrier(PETSC_COMM_WORLD));
    PetscCall(VecView(largevec, PETSC_VIEWER_STDOUT_WORLD));

    PetscCall(VecDestroy(&smallvec));
    PetscCall(DMRestoreGlobalVector(da, &largevec));
    PetscCall(ISDestroy(&patchis));
    PetscCall(VecScatterDestroy(&patchscat));
  }

  /* view the various parts */
  {
    for (i = 0; i < size; i++) {
      if (i == rank) {
        PetscCall(PetscPrintf(PETSC_COMM_SELF, "Processor %d: \n", i));
        PetscCall(DMView(subda[0], PETSC_VIEWER_STDOUT_SELF));
      }
      PetscCallMPI(MPI_Barrier(PETSC_COMM_WORLD));
    }

    PetscCall(DMGetLocalVector(subda[0], &slvec));
    PetscCall(DMGetGlobalVector(subda[0], &sgvec));
    PetscCall(DMGetGlobalVector(da, &v));

    /* test filling outer between the big DM and the small ones with the IS scatter*/
    PetscCall(VecScatterCreate(v, ois[0], sgvec, NULL, &oscata));

    PetscCall(FillLocalSubdomain(subda[0], sgvec));

    PetscCall(VecScatterBegin(oscata, sgvec, v, ADD_VALUES, SCATTER_REVERSE));
    PetscCall(VecScatterEnd(oscata, sgvec, v, ADD_VALUES, SCATTER_REVERSE));

    /* test the local-to-local scatter */

    /* fill up the local subdomain and then add them together */
    PetscCall(FillLocalSubdomain(da, v));

    PetscCall(VecScatterBegin(gscat[0], v, slvec, ADD_VALUES, SCATTER_FORWARD));
    PetscCall(VecScatterEnd(gscat[0], v, slvec, ADD_VALUES, SCATTER_FORWARD));

    PetscCall(VecView(v, PETSC_VIEWER_STDOUT_WORLD));

    /* test ghost scattering backwards */

    PetscCall(VecSet(v, 0));

    PetscCall(VecScatterBegin(gscat[0], slvec, v, ADD_VALUES, SCATTER_REVERSE));
    PetscCall(VecScatterEnd(gscat[0], slvec, v, ADD_VALUES, SCATTER_REVERSE));

    PetscCall(VecView(v, PETSC_VIEWER_STDOUT_WORLD));

    /* test overlap scattering backwards */

    PetscCall(DMLocalToGlobalBegin(subda[0], slvec, ADD_VALUES, sgvec));
    PetscCall(DMLocalToGlobalEnd(subda[0], slvec, ADD_VALUES, sgvec));

    PetscCall(VecSet(v, 0));

    PetscCall(VecScatterBegin(oscat[0], sgvec, v, ADD_VALUES, SCATTER_REVERSE));
    PetscCall(VecScatterEnd(oscat[0], sgvec, v, ADD_VALUES, SCATTER_REVERSE));

    PetscCall(VecView(v, PETSC_VIEWER_STDOUT_WORLD));

    /* test interior scattering backwards */

    PetscCall(VecSet(v, 0));

    PetscCall(VecScatterBegin(iscat[0], sgvec, v, ADD_VALUES, SCATTER_REVERSE));
    PetscCall(VecScatterEnd(iscat[0], sgvec, v, ADD_VALUES, SCATTER_REVERSE));

    PetscCall(VecView(v, PETSC_VIEWER_STDOUT_WORLD));

    /* test matrix allocation */
    for (i = 0; i < size; i++) {
      if (i == rank) {
        Mat m;
        PetscCall(PetscPrintf(PETSC_COMM_SELF, "Processor %d: \n", i));
        PetscCall(DMSetMatType(subda[0], MATAIJ));
        PetscCall(DMCreateMatrix(subda[0], &m));
        PetscCall(MatView(m, PETSC_VIEWER_STDOUT_SELF));
        PetscCall(MatDestroy(&m));
      }
      PetscCallMPI(MPI_Barrier(PETSC_COMM_WORLD));
    }
    PetscCall(DMRestoreLocalVector(subda[0], &slvec));
    PetscCall(DMRestoreGlobalVector(subda[0], &sgvec));
    PetscCall(DMRestoreGlobalVector(da, &v));
  }

  PetscCall(DMDestroy(&subda[0]));
  PetscCall(ISDestroy(&ois[0]));
  PetscCall(ISDestroy(&iis[0]));

  PetscCall(VecScatterDestroy(&iscat[0]));
  PetscCall(VecScatterDestroy(&oscat[0]));
  PetscCall(VecScatterDestroy(&gscat[0]));
  PetscCall(VecScatterDestroy(&oscata));

  PetscCall(PetscFree(iscat));
  PetscCall(PetscFree(oscat));
  PetscCall(PetscFree(gscat));
  PetscCall(PetscFree(oscata));

  PetscCall(PetscFree(subda));
  PetscCall(PetscFree(ois));
  PetscCall(PetscFree(iis));

  PetscCall(DMDestroy(&da));
  PetscCall(PetscFinalize());
  return 0;
}