xref: /petsc/src/dm/impls/plex/plexcreate.c (revision d62187667d71f95523d3bc2f58e5b0e6a69c5e76)

#define PETSCDM_DLL
#include <petsc/private/dmpleximpl.h>    /*I   "petscdmplex.h"   I*/
#include <petscdmda.h>
#include <petscsf.h>

/*@
  DMPlexCreateDoublet - Creates a mesh of two cells of the specified type, optionally with later refinement.

  Collective on MPI_Comm

  Input Parameters:
+ comm - The communicator for the DM object
. dim - The spatial dimension
. simplex - Flag for simplicial cells, otherwise they are tensor product cells
. interpolate - Flag to create intermediate mesh pieces (edges, faces)
. refinementUniform - Flag for uniform parallel refinement
- refinementLimit - A nonzero number indicates the largest admissible volume for a refined cell

  Output Parameter:
. dm  - The DM object

  Level: beginner

.keywords: DM, create
.seealso: DMSetType(), DMCreate()
@*/
PetscErrorCode DMPlexCreateDoublet(MPI_Comm comm, PetscInt dim, PetscBool simplex, PetscBool interpolate, PetscBool refinementUniform, PetscReal refinementLimit, DM *newdm)
{
  DM             dm;
  PetscInt       p;
  PetscMPIInt    rank;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  ierr = DMCreate(comm, &dm);CHKERRQ(ierr);
  ierr = DMSetType(dm, DMPLEX);CHKERRQ(ierr);
  ierr = DMSetDimension(dm, dim);CHKERRQ(ierr);
  ierr = MPI_Comm_rank(comm, &rank);CHKERRQ(ierr);
  switch (dim) {
  case 2:
    if (simplex) {ierr = PetscObjectSetName((PetscObject) dm, "triangular");CHKERRQ(ierr);}
    else         {ierr = PetscObjectSetName((PetscObject) dm, "quadrilateral");CHKERRQ(ierr);}
    break;
  case 3:
    if (simplex) {ierr = PetscObjectSetName((PetscObject) dm, "tetrahedral");CHKERRQ(ierr);}
    else         {ierr = PetscObjectSetName((PetscObject) dm, "hexahedral");CHKERRQ(ierr);}
    break;
  default:
    SETERRQ1(comm, PETSC_ERR_ARG_OUTOFRANGE, "Cannot make meshes for dimension %d", dim);
  }
  if (rank) {
    PetscInt numPoints[2] = {0, 0};
    ierr = DMPlexCreateFromDAG(dm, 1, numPoints, NULL, NULL, NULL, NULL);CHKERRQ(ierr);
  } else {
    switch (dim) {
    case 2:
      if (simplex) {
        PetscInt    numPoints[2]        = {4, 2};
        PetscInt    coneSize[6]         = {3, 3, 0, 0, 0, 0};
        PetscInt    cones[6]            = {2, 3, 4,  5, 4, 3};
        PetscInt    coneOrientations[6] = {0, 0, 0,  0, 0, 0};
        PetscScalar vertexCoords[8]     = {-0.5, 0.5, 0.0, 0.0, 0.0, 1.0, 0.5, 0.5};
        PetscInt    markerPoints[8]     = {2, 1, 3, 1, 4, 1, 5, 1};

        ierr = DMPlexCreateFromDAG(dm, 1, numPoints, coneSize, cones, coneOrientations, vertexCoords);CHKERRQ(ierr);
        for (p = 0; p < 4; ++p) {ierr = DMSetLabelValue(dm, "marker", markerPoints[p*2], markerPoints[p*2+1]);CHKERRQ(ierr);}
      } else {
        PetscInt    numPoints[2]        = {6, 2};
        PetscInt    coneSize[8]         = {4, 4, 0, 0, 0, 0, 0, 0};
        PetscInt    cones[8]            = {2, 3, 4, 5,  3, 6, 7, 4};
        PetscInt    coneOrientations[8] = {0, 0, 0, 0,  0, 0, 0, 0};
        PetscScalar vertexCoords[12]    = {-1.0, -0.5,  0.0, -0.5,  0.0, 0.5,  -1.0, 0.5,  1.0, -0.5,  1.0, 0.5};

        ierr = DMPlexCreateFromDAG(dm, 1, numPoints, coneSize, cones, coneOrientations, vertexCoords);CHKERRQ(ierr);
      }
      break;
    case 3:
      if (simplex) {
        PetscInt    numPoints[2]        = {5, 2};
        PetscInt    coneSize[7]         = {4, 4, 0, 0, 0, 0, 0};
        PetscInt    cones[8]            = {4, 3, 5, 2,  5, 3, 4, 6};
        PetscInt    coneOrientations[8] = {0, 0, 0, 0,  0, 0, 0, 0};
        PetscScalar vertexCoords[15]    = {-1.0, 0.0, 0.0,  0.0, -1.0, 0.0,  0.0, 0.0, 1.0,  0.0, 1.0, 0.0,  1.0, 0.0, 0.0};
        PetscInt    markerPoints[10]    = {2, 1, 3, 1, 4, 1, 5, 1, 6, 1};

        ierr = DMPlexCreateFromDAG(dm, 1, numPoints, coneSize, cones, coneOrientations, vertexCoords);CHKERRQ(ierr);
        for (p = 0; p < 5; ++p) {ierr = DMSetLabelValue(dm, "marker", markerPoints[p*2], markerPoints[p*2+1]);CHKERRQ(ierr);}
      } else {
        PetscInt    numPoints[2]         = {12, 2};
        PetscInt    coneSize[14]         = {8, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
        PetscInt    cones[16]            = {2, 3, 4, 5, 6, 7, 8, 9,  5, 4, 10, 11, 7, 12, 13, 8};
        PetscInt    coneOrientations[16] = {0, 0, 0, 0, 0, 0, 0, 0,  0, 0,  0,  0, 0,  0,  0, 0};
        PetscScalar vertexCoords[36]     = {-1.0, -0.5, -0.5,  -1.0,  0.5, -0.5,  0.0,  0.5, -0.5,   0.0, -0.5, -0.5,
                                            -1.0, -0.5,  0.5,   0.0, -0.5,  0.5,  0.0,  0.5,  0.5,  -1.0,  0.5,  0.5,
                                             1.0,  0.5, -0.5,   1.0, -0.5, -0.5,  1.0, -0.5,  0.5,   1.0,  0.5,  0.5};

        ierr = DMPlexCreateFromDAG(dm, 1, numPoints, coneSize, cones, coneOrientations, vertexCoords);CHKERRQ(ierr);
      }
      break;
    default:
      SETERRQ1(comm, PETSC_ERR_ARG_OUTOFRANGE, "Cannot make meshes for dimension %d", dim);
    }
  }
  *newdm = dm;
  if (refinementLimit > 0.0) {
    DM rdm;
    const char *name;

    ierr = DMPlexSetRefinementUniform(*newdm, PETSC_FALSE);CHKERRQ(ierr);
    ierr = DMPlexSetRefinementLimit(*newdm, refinementLimit);CHKERRQ(ierr);
    ierr = DMRefine(*newdm, comm, &rdm);CHKERRQ(ierr);
    ierr = PetscObjectGetName((PetscObject) *newdm, &name);CHKERRQ(ierr);
    ierr = PetscObjectSetName((PetscObject)    rdm,  name);CHKERRQ(ierr);
    ierr = DMDestroy(newdm);CHKERRQ(ierr);
    *newdm = rdm;
  }
  if (interpolate) {
    DM idm = NULL;
    const char *name;

    ierr = DMPlexInterpolate(*newdm, &idm);CHKERRQ(ierr);
    ierr = PetscObjectGetName((PetscObject) *newdm, &name);CHKERRQ(ierr);
    ierr = PetscObjectSetName((PetscObject)    idm,  name);CHKERRQ(ierr);
    ierr = DMPlexCopyCoordinates(*newdm, idm);CHKERRQ(ierr);
    ierr = DMCopyLabels(*newdm, idm);CHKERRQ(ierr);
    ierr = DMDestroy(newdm);CHKERRQ(ierr);
    *newdm = idm;
  }
  {
    DM refinedMesh     = NULL;
    DM distributedMesh = NULL;

    /* Distribute mesh over processes */
    ierr = DMPlexDistribute(*newdm, 0, NULL, &distributedMesh);CHKERRQ(ierr);
    if (distributedMesh) {
      ierr = DMDestroy(newdm);CHKERRQ(ierr);
      *newdm = distributedMesh;
    }
    if (refinementUniform) {
      ierr = DMPlexSetRefinementUniform(*newdm, refinementUniform);CHKERRQ(ierr);
      ierr = DMRefine(*newdm, comm, &refinedMesh);CHKERRQ(ierr);
      if (refinedMesh) {
        ierr = DMDestroy(newdm);CHKERRQ(ierr);
        *newdm = refinedMesh;
      }
    }
  }
  PetscFunctionReturn(0);
}

/*@
  DMPlexCreateSquareBoundary - Creates a 1D mesh the is the boundary of a square lattice.

  Collective on MPI_Comm

  Input Parameters:
+ comm  - The communicator for the DM object
. lower - The lower left corner coordinates
. upper - The upper right corner coordinates
- edges - The number of cells in each direction

  Output Parameter:
. dm  - The DM object

  Note: Here is the numbering returned for 2 cells in each direction:
$ 18--5-17--4--16
$  |     |     |
$  6    10     3
$  |     |     |
$ 19-11-20--9--15
$  |     |     |
$  7     8     2
$  |     |     |
$ 12--0-13--1--14

  Level: beginner

.keywords: DM, create
.seealso: DMPlexCreateBoxMesh(), DMPlexCreateCubeBoundary(), DMSetType(), DMCreate()
@*/
PetscErrorCode DMPlexCreateSquareBoundary(DM dm, const PetscReal lower[], const PetscReal upper[], const PetscInt edges[])
{
  const PetscInt numVertices    = (edges[0]+1)*(edges[1]+1);
  const PetscInt numEdges       = edges[0]*(edges[1]+1) + (edges[0]+1)*edges[1];
  PetscInt       markerTop      = 1;
  PetscInt       markerBottom   = 1;
  PetscInt       markerRight    = 1;
  PetscInt       markerLeft     = 1;
  PetscBool      markerSeparate = PETSC_FALSE;
  Vec            coordinates;
  PetscSection   coordSection;
  PetscScalar    *coords;
  PetscInt       coordSize;
  PetscMPIInt    rank;
  PetscInt       v, vx, vy;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  ierr = PetscOptionsGetBool(((PetscObject) dm)->options,((PetscObject) dm)->prefix, "-dm_plex_separate_marker", &markerSeparate, NULL);CHKERRQ(ierr);
  if (markerSeparate) {
    markerTop    = 3;
    markerBottom = 1;
    markerRight  = 2;
    markerLeft   = 4;
  }
  ierr = MPI_Comm_rank(PetscObjectComm((PetscObject)dm), &rank);CHKERRQ(ierr);
  if (!rank) {
    PetscInt e, ex, ey;

    ierr = DMPlexSetChart(dm, 0, numEdges+numVertices);CHKERRQ(ierr);
    for (e = 0; e < numEdges; ++e) {
      ierr = DMPlexSetConeSize(dm, e, 2);CHKERRQ(ierr);
    }
    ierr = DMSetUp(dm);CHKERRQ(ierr); /* Allocate space for cones */
    for (vx = 0; vx <= edges[0]; vx++) {
      for (ey = 0; ey < edges[1]; ey++) {
        PetscInt edge   = vx*edges[1] + ey + edges[0]*(edges[1]+1);
        PetscInt vertex = ey*(edges[0]+1) + vx + numEdges;
        PetscInt cone[2];

        cone[0] = vertex; cone[1] = vertex+edges[0]+1;
        ierr    = DMPlexSetCone(dm, edge, cone);CHKERRQ(ierr);
        if (vx == edges[0]) {
          ierr = DMSetLabelValue(dm, "marker", edge,    markerRight);CHKERRQ(ierr);
          ierr = DMSetLabelValue(dm, "marker", cone[0], markerRight);CHKERRQ(ierr);
          if (ey == edges[1]-1) {
            ierr = DMSetLabelValue(dm, "marker", cone[1], markerRight);CHKERRQ(ierr);
          }
        } else if (vx == 0) {
          ierr = DMSetLabelValue(dm, "marker", edge,    markerLeft);CHKERRQ(ierr);
          ierr = DMSetLabelValue(dm, "marker", cone[0], markerLeft);CHKERRQ(ierr);
          if (ey == edges[1]-1) {
            ierr = DMSetLabelValue(dm, "marker", cone[1], markerLeft);CHKERRQ(ierr);
          }
        }
      }
    }
    for (vy = 0; vy <= edges[1]; vy++) {
      for (ex = 0; ex < edges[0]; ex++) {
        PetscInt edge   = vy*edges[0]     + ex;
        PetscInt vertex = vy*(edges[0]+1) + ex + numEdges;
        PetscInt cone[2];

        cone[0] = vertex; cone[1] = vertex+1;
        ierr    = DMPlexSetCone(dm, edge, cone);CHKERRQ(ierr);
        if (vy == edges[1]) {
          ierr = DMSetLabelValue(dm, "marker", edge,    markerTop);CHKERRQ(ierr);
          ierr = DMSetLabelValue(dm, "marker", cone[0], markerTop);CHKERRQ(ierr);
          if (ex == edges[0]-1) {
            ierr = DMSetLabelValue(dm, "marker", cone[1], markerTop);CHKERRQ(ierr);
          }
        } else if (vy == 0) {
          ierr = DMSetLabelValue(dm, "marker", edge,    markerBottom);CHKERRQ(ierr);
          ierr = DMSetLabelValue(dm, "marker", cone[0], markerBottom);CHKERRQ(ierr);
          if (ex == edges[0]-1) {
            ierr = DMSetLabelValue(dm, "marker", cone[1], markerBottom);CHKERRQ(ierr);
          }
        }
      }
    }
  }
  ierr = DMPlexSymmetrize(dm);CHKERRQ(ierr);
  ierr = DMPlexStratify(dm);CHKERRQ(ierr);
  /* Build coordinates */
  ierr = DMGetCoordinateSection(dm, &coordSection);CHKERRQ(ierr);
  ierr = PetscSectionSetNumFields(coordSection, 1);CHKERRQ(ierr);
  ierr = PetscSectionSetChart(coordSection, numEdges, numEdges + numVertices);CHKERRQ(ierr);
  ierr = PetscSectionSetFieldComponents(coordSection, 0, 2);CHKERRQ(ierr);
  for (v = numEdges; v < numEdges+numVertices; ++v) {
    ierr = PetscSectionSetDof(coordSection, v, 2);CHKERRQ(ierr);
    ierr = PetscSectionSetFieldDof(coordSection, v, 0, 2);CHKERRQ(ierr);
  }
  ierr = PetscSectionSetUp(coordSection);CHKERRQ(ierr);
  ierr = PetscSectionGetStorageSize(coordSection, &coordSize);CHKERRQ(ierr);
  ierr = VecCreate(PETSC_COMM_SELF, &coordinates);CHKERRQ(ierr);
  ierr = PetscObjectSetName((PetscObject) coordinates, "coordinates");CHKERRQ(ierr);
  ierr = VecSetSizes(coordinates, coordSize, PETSC_DETERMINE);CHKERRQ(ierr);
  ierr = VecSetBlockSize(coordinates, 2);CHKERRQ(ierr);
  ierr = VecSetType(coordinates,VECSTANDARD);CHKERRQ(ierr);
  ierr = VecGetArray(coordinates, &coords);CHKERRQ(ierr);
  for (vy = 0; vy <= edges[1]; ++vy) {
    for (vx = 0; vx <= edges[0]; ++vx) {
      coords[(vy*(edges[0]+1)+vx)*2+0] = lower[0] + ((upper[0] - lower[0])/edges[0])*vx;
      coords[(vy*(edges[0]+1)+vx)*2+1] = lower[1] + ((upper[1] - lower[1])/edges[1])*vy;
    }
  }
  ierr = VecRestoreArray(coordinates, &coords);CHKERRQ(ierr);
  ierr = DMSetCoordinatesLocal(dm, coordinates);CHKERRQ(ierr);
  ierr = VecDestroy(&coordinates);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

/*@
  DMPlexCreateCubeBoundary - Creates a 2D mesh the is the boundary of a cubic lattice.

  Collective on MPI_Comm

  Input Parameters:
+ comm  - The communicator for the DM object
. lower - The lower left front corner coordinates
. upper - The upper right back corner coordinates
- edges - The number of cells in each direction

  Output Parameter:
. dm  - The DM object

  Level: beginner

.keywords: DM, create
.seealso: DMPlexCreateBoxMesh(), DMPlexCreateSquareBoundary(), DMSetType(), DMCreate()
@*/
PetscErrorCode DMPlexCreateCubeBoundary(DM dm, const PetscReal lower[], const PetscReal upper[], const PetscInt faces[])
{
  PetscInt       vertices[3], numVertices;
  PetscInt       numFaces    = 2*faces[0]*faces[1] + 2*faces[1]*faces[2] + 2*faces[0]*faces[2];
  Vec            coordinates;
  PetscSection   coordSection;
  PetscScalar    *coords;
  PetscInt       coordSize;
  PetscMPIInt    rank;
  PetscInt       v, vx, vy, vz;
  PetscInt       voffset, iface=0, cone[4];
  PetscErrorCode ierr;

  PetscFunctionBegin;
  if ((faces[0] < 1) || (faces[1] < 1) || (faces[2] < 1)) SETERRQ(PetscObjectComm((PetscObject)dm), PETSC_ERR_SUP, "Must have at least 1 face per side");
  ierr = MPI_Comm_rank(PetscObjectComm((PetscObject)dm), &rank);CHKERRQ(ierr);
  vertices[0] = faces[0]+1; vertices[1] = faces[1]+1; vertices[2] = faces[2]+1;
  numVertices = vertices[0]*vertices[1]*vertices[2];
  if (!rank) {
    PetscInt f;

    ierr = DMPlexSetChart(dm, 0, numFaces+numVertices);CHKERRQ(ierr);
    for (f = 0; f < numFaces; ++f) {
      ierr = DMPlexSetConeSize(dm, f, 4);CHKERRQ(ierr);
    }
    ierr = DMSetUp(dm);CHKERRQ(ierr); /* Allocate space for cones */
    for (v = 0; v < numFaces+numVertices; ++v) {
      ierr = DMSetLabelValue(dm, "marker", v, 1);CHKERRQ(ierr);
    }

    /* Side 0 (Top) */
    for (vy = 0; vy < faces[1]; vy++) {
      for (vx = 0; vx < faces[0]; vx++) {
        voffset = numFaces + vertices[0]*vertices[1]*(vertices[2]-1) + vy*vertices[0] + vx;
        cone[0] = voffset; cone[1] = voffset+1; cone[2] = voffset+vertices[0]+1; cone[3] = voffset+vertices[0];
        ierr    = DMPlexSetCone(dm, iface, cone);CHKERRQ(ierr);
        iface++;
      }
    }

    /* Side 1 (Bottom) */
    for (vy = 0; vy < faces[1]; vy++) {
      for (vx = 0; vx < faces[0]; vx++) {
        voffset = numFaces + vy*(faces[0]+1) + vx;
        cone[0] = voffset+1; cone[1] = voffset; cone[2] = voffset+vertices[0]; cone[3] = voffset+vertices[0]+1;
        ierr    = DMPlexSetCone(dm, iface, cone);CHKERRQ(ierr);
        iface++;
      }
    }

    /* Side 2 (Front) */
    for (vz = 0; vz < faces[2]; vz++) {
      for (vx = 0; vx < faces[0]; vx++) {
        voffset = numFaces + vz*vertices[0]*vertices[1] + vx;
        cone[0] = voffset; cone[1] = voffset+1; cone[2] = voffset+vertices[0]*vertices[1]+1; cone[3] = voffset+vertices[0]*vertices[1];
        ierr    = DMPlexSetCone(dm, iface, cone);CHKERRQ(ierr);
        iface++;
      }
    }

    /* Side 3 (Back) */
    for (vz = 0; vz < faces[2]; vz++) {
      for (vx = 0; vx < faces[0]; vx++) {
        voffset = numFaces + vz*vertices[0]*vertices[1] + vertices[0]*(vertices[1]-1) + vx;
        cone[0] = voffset+vertices[0]*vertices[1]; cone[1] = voffset+vertices[0]*vertices[1]+1;
        cone[2] = voffset+1; cone[3] = voffset;
        ierr    = DMPlexSetCone(dm, iface, cone);CHKERRQ(ierr);
        iface++;
      }
    }

    /* Side 4 (Left) */
    for (vz = 0; vz < faces[2]; vz++) {
      for (vy = 0; vy < faces[1]; vy++) {
        voffset = numFaces + vz*vertices[0]*vertices[1] + vy*vertices[0];
        cone[0] = voffset; cone[1] = voffset+vertices[0]*vertices[1];
        cone[2] = voffset+vertices[0]*vertices[1]+vertices[0]; cone[3] = voffset+vertices[0];
        ierr    = DMPlexSetCone(dm, iface, cone);CHKERRQ(ierr);
        iface++;
      }
    }

    /* Side 5 (Right) */
    for (vz = 0; vz < faces[2]; vz++) {
      for (vy = 0; vy < faces[1]; vy++) {
        voffset = numFaces + vz*vertices[0]*vertices[1] + vy*vertices[0] + vx;
        cone[0] = voffset+vertices[0]*vertices[1]; cone[1] = voffset;
        cone[2] = voffset+vertices[0]; cone[3] = voffset+vertices[0]*vertices[1]+vertices[0];
        ierr    = DMPlexSetCone(dm, iface, cone);CHKERRQ(ierr);
        iface++;
      }
    }
  }
  ierr = DMPlexSymmetrize(dm);CHKERRQ(ierr);
  ierr = DMPlexStratify(dm);CHKERRQ(ierr);
  /* Build coordinates */
  ierr = DMGetCoordinateSection(dm, &coordSection);CHKERRQ(ierr);
  ierr = PetscSectionSetChart(coordSection, numFaces, numFaces + numVertices);CHKERRQ(ierr);
  for (v = numFaces; v < numFaces+numVertices; ++v) {
    ierr = PetscSectionSetDof(coordSection, v, 3);CHKERRQ(ierr);
  }
  ierr = PetscSectionSetUp(coordSection);CHKERRQ(ierr);
  ierr = PetscSectionGetStorageSize(coordSection, &coordSize);CHKERRQ(ierr);
  ierr = VecCreate(PETSC_COMM_SELF, &coordinates);CHKERRQ(ierr);
  ierr = PetscObjectSetName((PetscObject) coordinates, "coordinates");CHKERRQ(ierr);
  ierr = VecSetSizes(coordinates, coordSize, PETSC_DETERMINE);CHKERRQ(ierr);
  ierr = VecSetBlockSize(coordinates, 3);CHKERRQ(ierr);
  ierr = VecSetType(coordinates,VECSTANDARD);CHKERRQ(ierr);
  ierr = VecGetArray(coordinates, &coords);CHKERRQ(ierr);
  for (vz = 0; vz <= faces[2]; ++vz) {
    for (vy = 0; vy <= faces[1]; ++vy) {
      for (vx = 0; vx <= faces[0]; ++vx) {
        coords[((vz*(faces[1]+1)+vy)*(faces[0]+1)+vx)*3+0] = lower[0] + ((upper[0] - lower[0])/faces[0])*vx;
        coords[((vz*(faces[1]+1)+vy)*(faces[0]+1)+vx)*3+1] = lower[1] + ((upper[1] - lower[1])/faces[1])*vy;
        coords[((vz*(faces[1]+1)+vy)*(faces[0]+1)+vx)*3+2] = lower[2] + ((upper[2] - lower[2])/faces[2])*vz;
      }
    }
  }
  ierr = VecRestoreArray(coordinates, &coords);CHKERRQ(ierr);
  ierr = DMSetCoordinatesLocal(dm, coordinates);CHKERRQ(ierr);
  ierr = VecDestroy(&coordinates);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

/*@
  DMPlexCreateBoxMesh - Creates a mesh on the tensor product of unit intervals (box) using simplices.

  Collective on MPI_Comm

  Input Parameters:
+ comm - The communicator for the DM object
. dim - The spatial dimension
. numFaces - Number of faces per dimension
- interpolate - Flag to create intermediate mesh pieces (edges, faces)

  Output Parameter:
. dm  - The DM object

  Level: beginner

.keywords: DM, create
.seealso: DMPlexCreateHexBoxMesh(), DMSetType(), DMCreate()
@*/
PetscErrorCode DMPlexCreateBoxMesh(MPI_Comm comm, PetscInt dim, PetscInt numFaces, PetscBool interpolate, DM *dm)
{
  DM             boundary;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  PetscValidPointer(dm, 4);
  ierr = DMCreate(comm, &boundary);CHKERRQ(ierr);
  PetscValidLogicalCollectiveInt(boundary,dim,2);
  ierr = DMSetType(boundary, DMPLEX);CHKERRQ(ierr);
  ierr = DMSetDimension(boundary, dim-1);CHKERRQ(ierr);
  ierr = DMSetCoordinateDim(boundary, dim);CHKERRQ(ierr);
  switch (dim) {
  case 2:
  {
    PetscReal lower[2] = {0.0, 0.0};
    PetscReal upper[2] = {1.0, 1.0};
    PetscInt  edges[2];

    edges[0] = numFaces; edges[1] = numFaces;
    ierr = DMPlexCreateSquareBoundary(boundary, lower, upper, edges);CHKERRQ(ierr);
    break;
  }
  case 3:
  {
    PetscReal lower[3] = {0.0, 0.0, 0.0};
    PetscReal upper[3] = {1.0, 1.0, 1.0};
    PetscInt  faces[3];

    faces[0] = numFaces; faces[1] = numFaces; faces[2] = numFaces;
    ierr = DMPlexCreateCubeBoundary(boundary, lower, upper, faces);CHKERRQ(ierr);
    break;
  }
  default:
    SETERRQ1(comm, PETSC_ERR_SUP, "Dimension not supported: %d", dim);
  }
  ierr = DMPlexGenerate(boundary, NULL, interpolate, dm);CHKERRQ(ierr);
  ierr = DMDestroy(&boundary);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

static PetscErrorCode DMPlexCreateCubeMesh_Internal(DM dm, const PetscReal lower[], const PetscReal upper[], const PetscInt edges[], DMBoundaryType bdX, DMBoundaryType bdY, DMBoundaryType bdZ)
{
  PetscInt       markerTop      = 1, faceMarkerTop      = 1;
  PetscInt       markerBottom   = 1, faceMarkerBottom   = 1;
  PetscInt       markerFront    = 1, faceMarkerFront    = 1;
  PetscInt       markerBack     = 1, faceMarkerBack     = 1;
  PetscInt       markerRight    = 1, faceMarkerRight    = 1;
  PetscInt       markerLeft     = 1, faceMarkerLeft     = 1;
  PetscInt       dim;
  PetscBool      markerSeparate = PETSC_FALSE;
  PetscMPIInt    rank;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  ierr = DMGetDimension(dm,&dim);CHKERRQ(ierr);
  ierr = MPI_Comm_rank(PetscObjectComm((PetscObject)dm), &rank);CHKERRQ(ierr);
  ierr = DMCreateLabel(dm,"marker");CHKERRQ(ierr);
  ierr = DMCreateLabel(dm,"Face Sets");CHKERRQ(ierr);
  switch (dim) {
  case 2:
    faceMarkerTop    = 3;
    faceMarkerBottom = 1;
    faceMarkerRight  = 2;
    faceMarkerLeft   = 4;
    break;
  case 3:
    faceMarkerBottom = 1;
    faceMarkerTop    = 2;
    faceMarkerFront  = 3;
    faceMarkerBack   = 4;
    faceMarkerRight  = 5;
    faceMarkerLeft   = 6;
    break;
  default:
    SETERRQ1(PETSC_COMM_SELF,PETSC_ERR_SUP,"Dimension %d not supported",dim);
    break;
  }
  ierr = PetscOptionsGetBool(((PetscObject) dm)->options,((PetscObject) dm)->prefix, "-dm_plex_separate_marker", &markerSeparate, NULL);CHKERRQ(ierr);
  if (markerSeparate) {
    markerBottom = faceMarkerBottom;
    markerTop    = faceMarkerTop;
    markerFront  = faceMarkerFront;
    markerBack   = faceMarkerBack;
    markerRight  = faceMarkerRight;
    markerLeft   = faceMarkerLeft;
  }
  {
    const PetscInt numXEdges    = !rank ? edges[0] : 0;
    const PetscInt numYEdges    = !rank ? edges[1] : 0;
    const PetscInt numZEdges    = !rank ? edges[2] : 0;
    const PetscInt numXVertices = !rank ? (bdX == DM_BOUNDARY_PERIODIC || bdX == DM_BOUNDARY_TWIST ? edges[0] : edges[0]+1) : 0;
    const PetscInt numYVertices = !rank ? (bdY == DM_BOUNDARY_PERIODIC || bdY == DM_BOUNDARY_TWIST ? edges[1] : edges[1]+1) : 0;
    const PetscInt numZVertices = !rank ? (bdZ == DM_BOUNDARY_PERIODIC || bdZ == DM_BOUNDARY_TWIST ? edges[2] : edges[2]+1) : 0;
    const PetscInt numCells     = numXEdges*numYEdges*numZEdges;
    const PetscInt numXFaces    = numYEdges*numZEdges;
    const PetscInt numYFaces    = numXEdges*numZEdges;
    const PetscInt numZFaces    = numXEdges*numYEdges;
    const PetscInt numTotXFaces = numXVertices*numXFaces;
    const PetscInt numTotYFaces = numYVertices*numYFaces;
    const PetscInt numTotZFaces = numZVertices*numZFaces;
    const PetscInt numFaces     = numTotXFaces + numTotYFaces + numTotZFaces;
    const PetscInt numTotXEdges = numXEdges*numYVertices*numZVertices;
    const PetscInt numTotYEdges = numYEdges*numXVertices*numZVertices;
    const PetscInt numTotZEdges = numZEdges*numXVertices*numYVertices;
    const PetscInt numVertices  = numXVertices*numYVertices*numZVertices;
    const PetscInt numEdges     = numTotXEdges + numTotYEdges + numTotZEdges;
    const PetscInt firstVertex  = (dim == 2) ? numFaces : numCells;
    const PetscInt firstXFace   = (dim == 2) ? 0 : numCells + numVertices;
    const PetscInt firstYFace   = firstXFace + numTotXFaces;
    const PetscInt firstZFace   = firstYFace + numTotYFaces;
    const PetscInt firstXEdge   = numCells + numFaces + numVertices;
    const PetscInt firstYEdge   = firstXEdge + numTotXEdges;
    const PetscInt firstZEdge   = firstYEdge + numTotYEdges;
    Vec            coordinates;
    PetscSection   coordSection;
    PetscScalar   *coords;
    PetscInt       coordSize;
    PetscInt       v, vx, vy, vz;
    PetscInt       c, f, fx, fy, fz, e, ex, ey, ez;

    ierr = DMPlexSetChart(dm, 0, numCells+numFaces+numEdges+numVertices);CHKERRQ(ierr);
    for (c = 0; c < numCells; c++) {
      ierr = DMPlexSetConeSize(dm, c, 6);CHKERRQ(ierr);
    }
    for (f = firstXFace; f < firstXFace+numFaces; ++f) {
      ierr = DMPlexSetConeSize(dm, f, 4);CHKERRQ(ierr);
    }
    for (e = firstXEdge; e < firstXEdge+numEdges; ++e) {
      ierr = DMPlexSetConeSize(dm, e, 2);CHKERRQ(ierr);
    }
    ierr = DMSetUp(dm);CHKERRQ(ierr); /* Allocate space for cones */
    /* Build cells */
    for (fz = 0; fz < numZEdges; ++fz) {
      for (fy = 0; fy < numYEdges; ++fy) {
        for (fx = 0; fx < numXEdges; ++fx) {
          PetscInt cell    = (fz*numYEdges + fy)*numXEdges + fx;
          PetscInt faceB   = firstZFace + (fy*numXEdges+fx)*numZVertices +   fz;
          PetscInt faceT   = firstZFace + (fy*numXEdges+fx)*numZVertices + ((fz+1)%numZVertices);
          PetscInt faceF   = firstYFace + (fz*numXEdges+fx)*numYVertices +   fy;
          PetscInt faceK   = firstYFace + (fz*numXEdges+fx)*numYVertices + ((fy+1)%numYVertices);
          PetscInt faceL   = firstXFace + (fz*numYEdges+fy)*numXVertices +   fx;
          PetscInt faceR   = firstXFace + (fz*numYEdges+fy)*numXVertices + ((fx+1)%numXVertices);
                            /* B,  T,  F,  K,  R,  L */
          PetscInt ornt[6] = {-4,  0,  0, -1,  0, -4}; /* ??? */
          PetscInt cone[6];

          /* no boundary twisting in 3D */
          cone[0] = faceB; cone[1] = faceT; cone[2] = faceF; cone[3] = faceK; cone[4] = faceR; cone[5] = faceL;
          ierr    = DMPlexSetCone(dm, cell, cone);CHKERRQ(ierr);
          ierr    = DMPlexSetConeOrientation(dm, cell, ornt);CHKERRQ(ierr);
        }
      }
    }
    /* Build x faces */
    for (fz = 0; fz < numZEdges; ++fz) {
      for (fy = 0; fy < numYEdges; ++fy) {
        for (fx = 0; fx < numXVertices; ++fx) {
          PetscInt face    = firstXFace + (fz*numYEdges+fy)*numXVertices + fx;
          PetscInt edgeL   = firstZEdge + (  fy*                 numXVertices+fx)*numZEdges + fz;
          PetscInt edgeR   = firstZEdge + (((fy+1)%numYVertices)*numXVertices+fx)*numZEdges + fz;
          PetscInt edgeB   = firstYEdge + (  fz*                 numXVertices+fx)*numYEdges + fy;
          PetscInt edgeT   = firstYEdge + (((fz+1)%numZVertices)*numXVertices+fx)*numYEdges + fy;
          PetscInt ornt[4] = {0, 0, -2, -2};
          PetscInt cone[4];

          if (dim == 3) {
            /* markers */
            if (bdX != DM_BOUNDARY_PERIODIC) {
              if (fx == numXVertices-1) {
                ierr = DMSetLabelValue(dm, "Face Sets", face, faceMarkerRight);CHKERRQ(ierr);
                ierr = DMSetLabelValue(dm, "marker", face, markerRight);CHKERRQ(ierr);
              }
              else if (fx == 0) {
                ierr = DMSetLabelValue(dm, "Face Sets", face, faceMarkerLeft);CHKERRQ(ierr);
                ierr = DMSetLabelValue(dm, "marker", face, markerLeft);CHKERRQ(ierr);
              }
            }
          }
          cone[0] = edgeB; cone[1] = edgeR; cone[2] = edgeT; cone[3] = edgeL;
          ierr    = DMPlexSetCone(dm, face, cone);CHKERRQ(ierr);
          ierr    = DMPlexSetConeOrientation(dm, face, ornt);CHKERRQ(ierr);
        }
      }
    }
    /* Build y faces */
    for (fz = 0; fz < numZEdges; ++fz) {
      for (fx = 0; fx < numXEdges; ++fx) {
        for (fy = 0; fy < numYVertices; ++fy) {
          PetscInt face    = firstYFace + (fz*numXEdges+fx)*numYVertices + fy;
          PetscInt edgeL   = firstZEdge + (fy*numXVertices+  fx                 )*numZEdges + fz;
          PetscInt edgeR   = firstZEdge + (fy*numXVertices+((fx+1)%numXVertices))*numZEdges + fz;
          PetscInt edgeB   = firstXEdge + (  fz                 *numYVertices+fy)*numXEdges + fx;
          PetscInt edgeT   = firstXEdge + (((fz+1)%numZVertices)*numYVertices+fy)*numXEdges + fx;
          PetscInt ornt[4] = {0, 0, -2, -2};
          PetscInt cone[4];

          if (dim == 3) {
            /* markers */
            if (bdY != DM_BOUNDARY_PERIODIC) {
              if (fy == numYVertices-1) {
                ierr = DMSetLabelValue(dm, "Face Sets", face, faceMarkerBack);CHKERRQ(ierr);
                ierr = DMSetLabelValue(dm, "marker", face, markerBack);CHKERRQ(ierr);
              }
              else if (fy == 0) {
                ierr = DMSetLabelValue(dm, "Face Sets", face, faceMarkerFront);CHKERRQ(ierr);
                ierr = DMSetLabelValue(dm, "marker", face, markerFront);CHKERRQ(ierr);
              }
            }
          }
          cone[0] = edgeB; cone[1] = edgeR; cone[2] = edgeT; cone[3] = edgeL;
          ierr    = DMPlexSetCone(dm, face, cone);CHKERRQ(ierr);
          ierr    = DMPlexSetConeOrientation(dm, face, ornt);CHKERRQ(ierr);
        }
      }
    }
    /* Build z faces */
    for (fy = 0; fy < numYEdges; ++fy) {
      for (fx = 0; fx < numXEdges; ++fx) {
        for (fz = 0; fz < numZVertices; fz++) {
          PetscInt face    = firstZFace + (fy*numXEdges+fx)*numZVertices + fz;
          PetscInt edgeL   = firstYEdge + (fz*numXVertices+  fx                 )*numYEdges + fy;
          PetscInt edgeR   = firstYEdge + (fz*numXVertices+((fx+1)%numXVertices))*numYEdges + fy;
          PetscInt edgeB   = firstXEdge + (fz*numYVertices+  fy                 )*numXEdges + fx;
          PetscInt edgeT   = firstXEdge + (fz*numYVertices+((fy+1)%numYVertices))*numXEdges + fx;
          PetscInt ornt[4] = {0, 0, -2, -2};
          PetscInt cone[4];

          if (dim == 2) {
            if (bdX == DM_BOUNDARY_TWIST && fx == numXEdges-1) {edgeR += numYEdges-1-2*fy; ornt[1] = -2;}
            if (bdY == DM_BOUNDARY_TWIST && fy == numYEdges-1) {edgeT += numXEdges-1-2*fx; ornt[2] =  0;}
          }
          else {
            /* markers */
            if (bdZ != DM_BOUNDARY_PERIODIC) {
              if (fz == numZVertices-1) {
                ierr = DMSetLabelValue(dm, "Face Sets", face, faceMarkerTop);CHKERRQ(ierr);
                ierr = DMSetLabelValue(dm, "marker", face, markerTop);CHKERRQ(ierr);
              }
              else if (fz == 0) {
                ierr = DMSetLabelValue(dm, "Face Sets", face, faceMarkerBottom);CHKERRQ(ierr);
                ierr = DMSetLabelValue(dm, "marker", face, markerBottom);CHKERRQ(ierr);
              }
            }
          }
          cone[0] = edgeB; cone[1] = edgeR; cone[2] = edgeT; cone[3] = edgeL;
          ierr    = DMPlexSetCone(dm, face, cone);CHKERRQ(ierr);
          ierr    = DMPlexSetConeOrientation(dm, face, ornt);CHKERRQ(ierr);
        }
      }
    }
    /* Build Z edges*/
    for (vy = 0; vy < numYVertices; vy++) {
      for (vx = 0; vx < numXVertices; vx++) {
        for (ez = 0; ez < numZEdges; ez++) {
          const PetscInt edge    = firstZEdge  + (vy*numXVertices+vx)*numZEdges + ez;
          const PetscInt vertexB = firstVertex + (  ez                 *numYVertices+vy)*numXVertices + vx;
          const PetscInt vertexT = firstVertex + (((ez+1)%numZVertices)*numYVertices+vy)*numXVertices + vx;
          PetscInt       cone[2];

          if (dim == 3) {
            if (bdX != DM_BOUNDARY_PERIODIC) {
              if (vx == numXVertices-1) {
                ierr = DMSetLabelValue(dm, "marker", edge, markerRight);CHKERRQ(ierr);
              }
              else if (vx == 0) {
                ierr = DMSetLabelValue(dm, "marker", edge, markerLeft);CHKERRQ(ierr);
              }
            }
            if (bdY != DM_BOUNDARY_PERIODIC) {
              if (vy == numYVertices-1) {
                ierr = DMSetLabelValue(dm, "marker", edge, markerBack);CHKERRQ(ierr);
              }
              else if (vy == 0) {
                ierr = DMSetLabelValue(dm, "marker", edge, markerFront);CHKERRQ(ierr);
              }
            }
          }
          cone[0] = vertexB; cone[1] = vertexT;
          ierr = DMPlexSetCone(dm, edge, cone);CHKERRQ(ierr);
        }
      }
    }
    /* Build Y edges*/
    for (vz = 0; vz < numZVertices; vz++) {
      for (vx = 0; vx < numXVertices; vx++) {
        for (ey = 0; ey < numYEdges; ey++) {
          const PetscInt nextv   = (dim == 2 && bdY == DM_BOUNDARY_TWIST && ey == numYEdges-1) ? (numXVertices-vx-1) : (vz*numYVertices+((ey+1)%numYVertices))*numXVertices + vx;
          const PetscInt edge    = firstYEdge  + (vz*numXVertices+vx)*numYEdges + ey;
          const PetscInt vertexF = firstVertex + (vz*numYVertices+ey)*numXVertices + vx;
          const PetscInt vertexK = firstVertex + nextv;
          PetscInt       cone[2];

          cone[0] = vertexF; cone[1] = vertexK;
          ierr = DMPlexSetCone(dm, edge, cone);CHKERRQ(ierr);
          if (dim == 2) {
            if ((bdX != DM_BOUNDARY_PERIODIC) && (bdX != DM_BOUNDARY_TWIST)) {
              if (vx == numXVertices-1) {
                ierr = DMSetLabelValue(dm, "Face Sets", edge, faceMarkerRight);CHKERRQ(ierr);
                ierr = DMSetLabelValue(dm, "marker", edge,    markerRight);CHKERRQ(ierr);
                ierr = DMSetLabelValue(dm, "marker", cone[0], markerRight);CHKERRQ(ierr);
                if (ey == numYEdges-1) {
                  ierr = DMSetLabelValue(dm, "marker", cone[1], markerRight);CHKERRQ(ierr);
                }
              }
              else if (vx == 0) {
                ierr = DMSetLabelValue(dm, "Face Sets", edge, faceMarkerLeft);CHKERRQ(ierr);
                ierr = DMSetLabelValue(dm, "marker", edge,    markerLeft);CHKERRQ(ierr);
                ierr = DMSetLabelValue(dm, "marker", cone[0], markerLeft);CHKERRQ(ierr);
                if (ey == numYEdges-1) {
                  ierr = DMSetLabelValue(dm, "marker", cone[1], markerLeft);CHKERRQ(ierr);
                }
              }
            }
          }
          else {
            if (bdX != DM_BOUNDARY_PERIODIC) {
              if (vx == numXVertices-1) {
                ierr = DMSetLabelValue(dm, "marker", edge, markerRight);CHKERRQ(ierr);
              }
              else if (vx == 0) {
                ierr = DMSetLabelValue(dm, "marker", edge, markerLeft);CHKERRQ(ierr);
              }
            }
            if (bdZ != DM_BOUNDARY_PERIODIC) {
              if (vz == numZVertices-1) {
                ierr = DMSetLabelValue(dm, "marker", edge, markerTop);CHKERRQ(ierr);
              }
              else if (vz == 0) {
                ierr = DMSetLabelValue(dm, "marker", edge, markerBottom);CHKERRQ(ierr);
              }
            }
          }
        }
      }
    }
    /* Build X edges*/
    for (vz = 0; vz < numZVertices; vz++) {
      for (vy = 0; vy < numYVertices; vy++) {
        for (ex = 0; ex < numXEdges; ex++) {
          const PetscInt nextv   = (dim == 2 && bdX == DM_BOUNDARY_TWIST && ex == numXEdges-1) ? (numYVertices-vy-1)*numXVertices : (vz*numYVertices+vy)*numXVertices + (ex+1)%numXVertices;
          const PetscInt edge    = firstXEdge  + (vz*numYVertices+vy)*numXEdges + ex;
          const PetscInt vertexL = firstVertex + (vz*numYVertices+vy)*numXVertices + ex;
          const PetscInt vertexR = firstVertex + nextv;
          PetscInt       cone[2];

          cone[0] = vertexL; cone[1] = vertexR;
          ierr = DMPlexSetCone(dm, edge, cone);CHKERRQ(ierr);
          if (dim == 2) {
            if ((bdY != DM_BOUNDARY_PERIODIC) && (bdY != DM_BOUNDARY_TWIST)) {
              if (vy == numYVertices-1) {
                ierr = DMSetLabelValue(dm, "Face Sets", edge, faceMarkerTop);CHKERRQ(ierr);
                ierr = DMSetLabelValue(dm, "marker", edge,    markerTop);CHKERRQ(ierr);
                ierr = DMSetLabelValue(dm, "marker", cone[0], markerTop);CHKERRQ(ierr);
                if (ex == numXEdges-1) {
                  ierr = DMSetLabelValue(dm, "marker", cone[1], markerTop);CHKERRQ(ierr);
                }
              }
              else if (vy == 0) {
                ierr = DMSetLabelValue(dm, "Face Sets", edge, faceMarkerBottom);CHKERRQ(ierr);
                ierr = DMSetLabelValue(dm, "marker", edge,    markerBottom);CHKERRQ(ierr);
                ierr = DMSetLabelValue(dm, "marker", cone[0], markerBottom);CHKERRQ(ierr);
                if (ex == numXEdges-1) {
                  ierr = DMSetLabelValue(dm, "marker", cone[1], markerBottom);CHKERRQ(ierr);
                }
              }
            }
          }
          else {
            if (bdY != DM_BOUNDARY_PERIODIC) {
              if (vy == numYVertices-1) {
                ierr = DMSetLabelValue(dm, "marker", edge, markerBack);CHKERRQ(ierr);
              }
              else if (vy == 0) {
                ierr = DMSetLabelValue(dm, "marker", edge, markerFront);CHKERRQ(ierr);
              }
            }
            if (bdZ != DM_BOUNDARY_PERIODIC) {
              if (vz == numZVertices-1) {
                ierr = DMSetLabelValue(dm, "marker", edge, markerTop);CHKERRQ(ierr);
              }
              else if (vz == 0) {
                ierr = DMSetLabelValue(dm, "marker", edge, markerBottom);CHKERRQ(ierr);
              }
            }
          }
        }
      }
    }
    ierr = DMPlexSymmetrize(dm);CHKERRQ(ierr);
    ierr = DMPlexStratify(dm);CHKERRQ(ierr);
    /* Build coordinates */
    ierr = DMGetCoordinateSection(dm, &coordSection);CHKERRQ(ierr);
    ierr = PetscSectionSetNumFields(coordSection, 1);CHKERRQ(ierr);
    ierr = PetscSectionSetFieldComponents(coordSection, 0, dim);CHKERRQ(ierr);
    ierr = PetscSectionSetChart(coordSection, firstVertex, firstVertex+numVertices);CHKERRQ(ierr);
    for (v = firstVertex; v < firstVertex+numVertices; ++v) {
      ierr = PetscSectionSetDof(coordSection, v, dim);CHKERRQ(ierr);
      ierr = PetscSectionSetFieldDof(coordSection, v, 0, dim);CHKERRQ(ierr);
    }
    ierr = PetscSectionSetUp(coordSection);CHKERRQ(ierr);
    ierr = PetscSectionGetStorageSize(coordSection, &coordSize);CHKERRQ(ierr);
    ierr = VecCreate(PETSC_COMM_SELF, &coordinates);CHKERRQ(ierr);
    ierr = PetscObjectSetName((PetscObject) coordinates, "coordinates");CHKERRQ(ierr);
    ierr = VecSetSizes(coordinates, coordSize, PETSC_DETERMINE);CHKERRQ(ierr);
    ierr = VecSetBlockSize(coordinates, dim);CHKERRQ(ierr);
    ierr = VecSetType(coordinates,VECSTANDARD);CHKERRQ(ierr);
    ierr = VecGetArray(coordinates, &coords);CHKERRQ(ierr);
    for (vz = 0; vz < numZVertices; ++vz) {
      for (vy = 0; vy < numYVertices; ++vy) {
        for (vx = 0; vx < numXVertices; ++vx) {
          coords[((vz*numYVertices+vy)*numXVertices+vx)*dim+0] = lower[0] + ((upper[0] - lower[0])/numXEdges)*vx;
          coords[((vz*numYVertices+vy)*numXVertices+vx)*dim+1] = lower[1] + ((upper[1] - lower[1])/numYEdges)*vy;
          if (dim == 3) {
            coords[((vz*numYVertices+vy)*numXVertices+vx)*dim+2] = lower[2] + ((upper[2] - lower[2])/numZEdges)*vz;
          }
        }
      }
    }
    ierr = VecRestoreArray(coordinates, &coords);CHKERRQ(ierr);
    ierr = DMSetCoordinatesLocal(dm, coordinates);CHKERRQ(ierr);
    ierr = VecDestroy(&coordinates);CHKERRQ(ierr);
  }
  PetscFunctionReturn(0);
}

/*@
  DMPlexCreateHexBoxMesh - Creates a mesh on the tensor product of unit intervals (box) using hexahedra.

  Collective on MPI_Comm

  Input Parameters:
+ comm  - The communicator for the DM object
. dim   - The spatial dimension
. periodicX - The boundary type for the X direction
. periodicY - The boundary type for the Y direction
. periodicZ - The boundary type for the Z direction
- cells - The number of cells in each direction

  Output Parameter:
. dm  - The DM object

  Note: Here is the numbering returned for 2 cells in each direction:
$ 22--8-23--9--24
$  |     |     |
$ 13  2 14  3  15
$  |     |     |
$ 19--6-20--7--21
$  |     |     |
$ 10  0 11  1 12
$  |     |     |
$ 16--4-17--5--18

  Level: beginner

.keywords: DM, create
.seealso: DMPlexCreateBoxMesh(), DMSetType(), DMCreate()
@*/
PetscErrorCode DMPlexCreateHexBoxMesh(MPI_Comm comm, PetscInt dim, const PetscInt cells[], DMBoundaryType periodicX, DMBoundaryType periodicY, DMBoundaryType periodicZ, DM *dm)
{
  PetscInt       i;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  PetscValidPointer(dm, 7);
  ierr = DMCreate(comm, dm);CHKERRQ(ierr);
  PetscValidLogicalCollectiveInt(*dm,dim,2);
  ierr = DMSetType(*dm, DMPLEX);CHKERRQ(ierr);
  ierr = DMSetDimension(*dm, dim);CHKERRQ(ierr);
  switch (dim) {
  case 2:
  {
    PetscReal lower[3] = {0.0, 0.0, 0.0};
    PetscReal upper[3] = {1.0, 1.0, 0.0};

    ierr = DMPlexCreateCubeMesh_Internal(*dm, lower, upper, cells, periodicX, periodicY, DM_BOUNDARY_NONE);CHKERRQ(ierr);
    if (periodicX == DM_BOUNDARY_PERIODIC || periodicX == DM_BOUNDARY_TWIST ||
        periodicY == DM_BOUNDARY_PERIODIC || periodicY == DM_BOUNDARY_TWIST) {
      PetscReal      L[2];
      PetscReal      maxCell[2];
      DMBoundaryType bdType[2];

      bdType[0] = periodicX;
      bdType[1] = periodicY;
      for (i = 0; i < dim; i++) {
        L[i]       = upper[i] - lower[i];
        maxCell[i] = 1.1 * (L[i] / cells[i]);
      }

      ierr = DMSetPeriodicity(*dm,maxCell,L,bdType);CHKERRQ(ierr);
    }
    break;
  }
  case 3:
  {
    PetscReal lower[3] = {0.0, 0.0, 0.0};
    PetscReal upper[3] = {1.0, 1.0, 1.0};

    ierr = DMPlexCreateCubeMesh_Internal(*dm, lower, upper, cells, periodicX, periodicY, periodicZ);CHKERRQ(ierr);
    if (periodicX == DM_BOUNDARY_PERIODIC || periodicX == DM_BOUNDARY_TWIST ||
        periodicY == DM_BOUNDARY_PERIODIC || periodicY == DM_BOUNDARY_TWIST ||
        periodicZ == DM_BOUNDARY_PERIODIC || periodicZ == DM_BOUNDARY_TWIST) {
      PetscReal      L[3];
      PetscReal      maxCell[3];
      DMBoundaryType bdType[3];

      bdType[0] = periodicX;
      bdType[1] = periodicY;
      bdType[2] = periodicZ;
      for (i = 0; i < dim; i++) {
        L[i]       = upper[i] - lower[i];
        maxCell[i] = 1.1 * (L[i] / cells[i]);
      }

      ierr = DMSetPeriodicity(*dm,maxCell,L,bdType);CHKERRQ(ierr);
    }
    break;
  }
  default:
    SETERRQ1(comm, PETSC_ERR_SUP, "Dimension not supported: %d", dim);
  }
  PetscFunctionReturn(0);
}

/* External function declarations here */
extern PetscErrorCode DMCreateInterpolation_Plex(DM dmCoarse, DM dmFine, Mat *interpolation, Vec *scaling);
extern PetscErrorCode DMCreateInjection_Plex(DM dmCoarse, DM dmFine, Mat *mat);
extern PetscErrorCode DMCreateDefaultSection_Plex(DM dm);
extern PetscErrorCode DMCreateDefaultConstraints_Plex(DM dm);
extern PetscErrorCode DMCreateMatrix_Plex(DM dm,  Mat *J);
extern PetscErrorCode DMCreateCoordinateDM_Plex(DM dm, DM *cdm);
PETSC_INTERN PetscErrorCode DMClone_Plex(DM dm, DM *newdm);
extern PetscErrorCode DMSetUp_Plex(DM dm);
extern PetscErrorCode DMDestroy_Plex(DM dm);
extern PetscErrorCode DMView_Plex(DM dm, PetscViewer viewer);
extern PetscErrorCode DMLoad_Plex(DM dm, PetscViewer viewer);
extern PetscErrorCode DMCreateSubDM_Plex(DM dm, PetscInt numFields, PetscInt fields[], IS *is, DM *subdm);

/* Replace dm with the contents of dmNew
   - Share the DM_Plex structure
   - Share the coordinates
   - Share the SF
*/
static PetscErrorCode DMPlexReplace_Static(DM dm, DM dmNew)
{
  PetscSF          sf;
  DM               coordDM, coarseDM;
  Vec              coords;
  const PetscReal *maxCell, *L;
  const DMBoundaryType *bd;
  PetscErrorCode   ierr;

  PetscFunctionBegin;
  ierr = DMGetPointSF(dmNew, &sf);CHKERRQ(ierr);
  ierr = DMSetPointSF(dm, sf);CHKERRQ(ierr);
  ierr = DMGetCoordinateDM(dmNew, &coordDM);CHKERRQ(ierr);
  ierr = DMGetCoordinatesLocal(dmNew, &coords);CHKERRQ(ierr);
  ierr = DMSetCoordinateDM(dm, coordDM);CHKERRQ(ierr);
  ierr = DMSetCoordinatesLocal(dm, coords);CHKERRQ(ierr);
  ierr = DMGetPeriodicity(dm, &maxCell, &L, &bd);CHKERRQ(ierr);
  if (L) {ierr = DMSetPeriodicity(dmNew, maxCell, L, bd);CHKERRQ(ierr);}
  ierr = DMDestroy_Plex(dm);CHKERRQ(ierr);
  dm->data = dmNew->data;
  ((DM_Plex *) dmNew->data)->refct++;
  dmNew->labels->refct++;
  if (!--(dm->labels->refct)) {
    DMLabelLink next = dm->labels->next;

    /* destroy the labels */
    while (next) {
      DMLabelLink tmp = next->next;

      ierr = DMLabelDestroy(&next->label);CHKERRQ(ierr);
      ierr = PetscFree(next);CHKERRQ(ierr);
      next = tmp;
    }
    ierr = PetscFree(dm->labels);CHKERRQ(ierr);
  }
  dm->labels = dmNew->labels;
  dm->depthLabel = dmNew->depthLabel;
  ierr = DMGetCoarseDM(dmNew,&coarseDM);CHKERRQ(ierr);
  ierr = DMSetCoarseDM(dm,coarseDM);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

/* Swap dm with the contents of dmNew
   - Swap the DM_Plex structure
   - Swap the coordinates
   - Swap the point PetscSF
*/
static PetscErrorCode DMPlexSwap_Static(DM dmA, DM dmB)
{
  DM              coordDMA, coordDMB;
  Vec             coordsA,  coordsB;
  PetscSF         sfA,      sfB;
  void            *tmp;
  DMLabelLinkList listTmp;
  DMLabel         depthTmp;
  PetscErrorCode  ierr;

  PetscFunctionBegin;
  ierr = DMGetPointSF(dmA, &sfA);CHKERRQ(ierr);
  ierr = DMGetPointSF(dmB, &sfB);CHKERRQ(ierr);
  ierr = PetscObjectReference((PetscObject) sfA);CHKERRQ(ierr);
  ierr = DMSetPointSF(dmA, sfB);CHKERRQ(ierr);
  ierr = DMSetPointSF(dmB, sfA);CHKERRQ(ierr);
  ierr = PetscObjectDereference((PetscObject) sfA);CHKERRQ(ierr);

  ierr = DMGetCoordinateDM(dmA, &coordDMA);CHKERRQ(ierr);
  ierr = DMGetCoordinateDM(dmB, &coordDMB);CHKERRQ(ierr);
  ierr = PetscObjectReference((PetscObject) coordDMA);CHKERRQ(ierr);
  ierr = DMSetCoordinateDM(dmA, coordDMB);CHKERRQ(ierr);
  ierr = DMSetCoordinateDM(dmB, coordDMA);CHKERRQ(ierr);
  ierr = PetscObjectDereference((PetscObject) coordDMA);CHKERRQ(ierr);

  ierr = DMGetCoordinatesLocal(dmA, &coordsA);CHKERRQ(ierr);
  ierr = DMGetCoordinatesLocal(dmB, &coordsB);CHKERRQ(ierr);
  ierr = PetscObjectReference((PetscObject) coordsA);CHKERRQ(ierr);
  ierr = DMSetCoordinatesLocal(dmA, coordsB);CHKERRQ(ierr);
  ierr = DMSetCoordinatesLocal(dmB, coordsA);CHKERRQ(ierr);
  ierr = PetscObjectDereference((PetscObject) coordsA);CHKERRQ(ierr);

  tmp       = dmA->data;
  dmA->data = dmB->data;
  dmB->data = tmp;
  listTmp   = dmA->labels;
  dmA->labels = dmB->labels;
  dmB->labels = listTmp;
  depthTmp  = dmA->depthLabel;
  dmA->depthLabel = dmB->depthLabel;
  dmB->depthLabel = depthTmp;
  PetscFunctionReturn(0);
}

PetscErrorCode DMSetFromOptions_NonRefinement_Plex(PetscOptionItems *PetscOptionsObject,DM dm)
{
  DM_Plex       *mesh = (DM_Plex*) dm->data;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  /* Handle viewing */
  ierr = PetscOptionsBool("-dm_plex_print_set_values", "Output all set values info", "DMView", PETSC_FALSE, &mesh->printSetValues, NULL);CHKERRQ(ierr);
  ierr = PetscOptionsInt("-dm_plex_print_fem", "Debug output level all fem computations", "DMView", 0, &mesh->printFEM, NULL);CHKERRQ(ierr);
  ierr = PetscOptionsReal("-dm_plex_print_tol", "Tolerance for FEM output", "DMView", mesh->printTol, &mesh->printTol, NULL);CHKERRQ(ierr);
  /* Point Location */
  ierr = PetscOptionsBool("-dm_plex_hash_location", "Use grid hashing for point location", "DMView", PETSC_FALSE, &mesh->useHashLocation, NULL);CHKERRQ(ierr);
  /* Generation and remeshing */
  ierr = PetscOptionsBool("-dm_plex_remesh_bd", "Allow changes to the boundary on remeshing", "DMView", PETSC_FALSE, &mesh->remeshBd, NULL);CHKERRQ(ierr);
  /* Projection behavior */
  ierr = PetscOptionsInt("-dm_plex_max_projection_height", "Maxmimum mesh point height used to project locally", "DMPlexSetMaxProjectionHeight", 0, &mesh->maxProjectionHeight, NULL);CHKERRQ(ierr);
  ierr = PetscOptionsBool("-dm_plex_regular_refinement", "Use special nested projection algorithm for regular refinement", "DMPlexSetRegularRefinement", mesh->regularRefinement, &mesh->regularRefinement, NULL);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

static PetscErrorCode DMSetFromOptions_Plex(PetscOptionItems *PetscOptionsObject,DM dm)
{
  PetscInt       refine = 0, coarsen = 0, r;
  PetscBool      isHierarchy;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  PetscValidHeaderSpecific(dm, DM_CLASSID, 1);
  ierr = PetscOptionsHead(PetscOptionsObject,"DMPlex Options");CHKERRQ(ierr);
  /* Handle DMPlex refinement */
  ierr = PetscOptionsInt("-dm_refine", "The number of uniform refinements", "DMCreate", refine, &refine, NULL);CHKERRQ(ierr);
  ierr = PetscOptionsInt("-dm_refine_hierarchy", "The number of uniform refinements", "DMCreate", refine, &refine, &isHierarchy);CHKERRQ(ierr);
  if (refine) {ierr = DMPlexSetRefinementUniform(dm, PETSC_TRUE);CHKERRQ(ierr);}
  if (refine && isHierarchy) {
    DM *dms, coarseDM;

    ierr = DMGetCoarseDM(dm, &coarseDM);CHKERRQ(ierr);
    ierr = PetscObjectReference((PetscObject)coarseDM);CHKERRQ(ierr);
    ierr = PetscMalloc1(refine,&dms);CHKERRQ(ierr);
    ierr = DMRefineHierarchy(dm, refine, dms);CHKERRQ(ierr);
    /* Total hack since we do not pass in a pointer */
    ierr = DMPlexSwap_Static(dm, dms[refine-1]);CHKERRQ(ierr);
    if (refine == 1) {
      ierr = DMSetCoarseDM(dm, dms[0]);CHKERRQ(ierr);
      ierr = DMPlexSetRegularRefinement(dm, PETSC_TRUE);CHKERRQ(ierr);
    } else {
      ierr = DMSetCoarseDM(dm, dms[refine-2]);CHKERRQ(ierr);
      ierr = DMPlexSetRegularRefinement(dm, PETSC_TRUE);CHKERRQ(ierr);
      ierr = DMSetCoarseDM(dms[0], dms[refine-1]);CHKERRQ(ierr);
      ierr = DMPlexSetRegularRefinement(dms[0], PETSC_TRUE);CHKERRQ(ierr);
    }
    ierr = DMSetCoarseDM(dms[refine-1], coarseDM);CHKERRQ(ierr);
    ierr = PetscObjectDereference((PetscObject)coarseDM);CHKERRQ(ierr);
    /* Free DMs */
    for (r = 0; r < refine; ++r) {
      ierr = DMSetFromOptions_NonRefinement_Plex(PetscOptionsObject, dms[r]);CHKERRQ(ierr);
      ierr = DMDestroy(&dms[r]);CHKERRQ(ierr);
    }
    ierr = PetscFree(dms);CHKERRQ(ierr);
  } else {
    for (r = 0; r < refine; ++r) {
      DM refinedMesh;

      ierr = DMSetFromOptions_NonRefinement_Plex(PetscOptionsObject, dm);CHKERRQ(ierr);
      ierr = DMRefine(dm, PetscObjectComm((PetscObject) dm), &refinedMesh);CHKERRQ(ierr);
      /* Total hack since we do not pass in a pointer */
      ierr = DMPlexReplace_Static(dm, refinedMesh);CHKERRQ(ierr);
      ierr = DMSetFromOptions_NonRefinement_Plex(PetscOptionsObject, dm);CHKERRQ(ierr);
      ierr = DMDestroy(&refinedMesh);CHKERRQ(ierr);
    }
  }
  /* Handle DMPlex coarsening */
  ierr = PetscOptionsInt("-dm_coarsen", "Coarsen the mesh", "DMCreate", coarsen, &coarsen, NULL);CHKERRQ(ierr);
  ierr = PetscOptionsInt("-dm_coarsen_hierarchy", "The number of coarsenings", "DMCreate", coarsen, &coarsen, &isHierarchy);CHKERRQ(ierr);
  if (coarsen && isHierarchy) {
    DM *dms;

    ierr = PetscMalloc1(coarsen, &dms);CHKERRQ(ierr);
    ierr = DMCoarsenHierarchy(dm, coarsen, dms);CHKERRQ(ierr);
    /* Free DMs */
    for (r = 0; r < coarsen; ++r) {
      ierr = DMSetFromOptions_NonRefinement_Plex(PetscOptionsObject, dms[r]);CHKERRQ(ierr);
      ierr = DMDestroy(&dms[r]);CHKERRQ(ierr);
    }
    ierr = PetscFree(dms);CHKERRQ(ierr);
  } else {
    for (r = 0; r < coarsen; ++r) {
      DM coarseMesh;

      ierr = DMSetFromOptions_NonRefinement_Plex(PetscOptionsObject, dm);CHKERRQ(ierr);
      ierr = DMCoarsen(dm, PetscObjectComm((PetscObject) dm), &coarseMesh);CHKERRQ(ierr);
      /* Total hack since we do not pass in a pointer */
      ierr = DMPlexReplace_Static(dm, coarseMesh);CHKERRQ(ierr);
      ierr = DMSetFromOptions_NonRefinement_Plex(PetscOptionsObject, dm);CHKERRQ(ierr);
      ierr = DMDestroy(&coarseMesh);CHKERRQ(ierr);
    }
  }
  /* Handle */
  ierr = DMSetFromOptions_NonRefinement_Plex(PetscOptionsObject, dm);CHKERRQ(ierr);
  ierr = PetscOptionsTail();CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

static PetscErrorCode DMCreateGlobalVector_Plex(DM dm,Vec *vec)
{
  PetscErrorCode ierr;

  PetscFunctionBegin;
  ierr = DMCreateGlobalVector_Section_Private(dm,vec);CHKERRQ(ierr);
  /* ierr = VecSetOperation(*vec, VECOP_DUPLICATE, (void(*)(void)) VecDuplicate_MPI_DM);CHKERRQ(ierr); */
  ierr = VecSetOperation(*vec, VECOP_VIEW, (void (*)(void)) VecView_Plex);CHKERRQ(ierr);
  ierr = VecSetOperation(*vec, VECOP_VIEWNATIVE, (void (*)(void)) VecView_Plex_Native);CHKERRQ(ierr);
  ierr = VecSetOperation(*vec, VECOP_LOAD, (void (*)(void)) VecLoad_Plex);CHKERRQ(ierr);
  ierr = VecSetOperation(*vec, VECOP_LOADNATIVE, (void (*)(void)) VecLoad_Plex_Native);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

static PetscErrorCode DMCreateLocalVector_Plex(DM dm,Vec *vec)
{
  PetscErrorCode ierr;

  PetscFunctionBegin;
  ierr = DMCreateLocalVector_Section_Private(dm,vec);CHKERRQ(ierr);
  ierr = VecSetOperation(*vec, VECOP_VIEW, (void (*)(void)) VecView_Plex_Local);CHKERRQ(ierr);
  ierr = VecSetOperation(*vec, VECOP_LOAD, (void (*)(void)) VecLoad_Plex_Local);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

static PetscErrorCode DMGetDimPoints_Plex(DM dm, PetscInt dim, PetscInt *pStart, PetscInt *pEnd)
{
  PetscInt       depth, d;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  ierr = DMPlexGetDepth(dm, &depth);CHKERRQ(ierr);
  if (depth == 1) {
    ierr = DMGetDimension(dm, &d);CHKERRQ(ierr);
    if (dim == 0)      {ierr = DMPlexGetDepthStratum(dm, dim, pStart, pEnd);CHKERRQ(ierr);}
    else if (dim == d) {ierr = DMPlexGetDepthStratum(dm, 1, pStart, pEnd);CHKERRQ(ierr);}
    else               {*pStart = 0; *pEnd = 0;}
  } else {
    ierr = DMPlexGetDepthStratum(dm, dim, pStart, pEnd);CHKERRQ(ierr);
  }
  PetscFunctionReturn(0);
}

static PetscErrorCode DMGetNeighors_Plex(DM dm, PetscInt *nranks, const PetscMPIInt *ranks[])
{
  PetscSF        sf;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  ierr = DMGetPointSF(dm, &sf);CHKERRQ(ierr);
  ierr = PetscSFGetRanks(sf, nranks, ranks, NULL, NULL, NULL);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

static PetscErrorCode DMInitialize_Plex(DM dm)
{
  PetscErrorCode ierr;

  PetscFunctionBegin;
  dm->ops->view                            = DMView_Plex;
  dm->ops->load                            = DMLoad_Plex;
  dm->ops->setfromoptions                  = DMSetFromOptions_Plex;
  dm->ops->clone                           = DMClone_Plex;
  dm->ops->setup                           = DMSetUp_Plex;
  dm->ops->createdefaultsection            = DMCreateDefaultSection_Plex;
  dm->ops->createdefaultconstraints        = DMCreateDefaultConstraints_Plex;
  dm->ops->createglobalvector              = DMCreateGlobalVector_Plex;
  dm->ops->createlocalvector               = DMCreateLocalVector_Plex;
  dm->ops->getlocaltoglobalmapping         = NULL;
  dm->ops->createfieldis                   = NULL;
  dm->ops->createcoordinatedm              = DMCreateCoordinateDM_Plex;
  dm->ops->getcoloring                     = NULL;
  dm->ops->creatematrix                    = DMCreateMatrix_Plex;
  dm->ops->createinterpolation             = DMCreateInterpolation_Plex;
  dm->ops->getaggregates                   = NULL;
  dm->ops->getinjection                    = DMCreateInjection_Plex;
  dm->ops->refine                          = DMRefine_Plex;
  dm->ops->coarsen                         = DMCoarsen_Plex;
  dm->ops->refinehierarchy                 = DMRefineHierarchy_Plex;
  dm->ops->coarsenhierarchy                = DMCoarsenHierarchy_Plex;
  dm->ops->globaltolocalbegin              = NULL;
  dm->ops->globaltolocalend                = NULL;
  dm->ops->localtoglobalbegin              = NULL;
  dm->ops->localtoglobalend                = NULL;
  dm->ops->destroy                         = DMDestroy_Plex;
  dm->ops->createsubdm                     = DMCreateSubDM_Plex;
  dm->ops->getdimpoints                    = DMGetDimPoints_Plex;
  dm->ops->locatepoints                    = DMLocatePoints_Plex;
  dm->ops->projectfunctionlocal            = DMProjectFunctionLocal_Plex;
  dm->ops->projectfunctionlabellocal       = DMProjectFunctionLabelLocal_Plex;
  dm->ops->projectfieldlocal               = DMProjectFieldLocal_Plex;
  dm->ops->projectfieldlabellocal          = DMProjectFieldLabelLocal_Plex;
  dm->ops->computel2diff                   = DMComputeL2Diff_Plex;
  dm->ops->computel2gradientdiff           = DMComputeL2GradientDiff_Plex;
  dm->ops->computel2fielddiff              = DMComputeL2FieldDiff_Plex;
  dm->ops->getneighbors                    = DMGetNeighors_Plex;
  ierr = PetscObjectComposeFunction((PetscObject)dm,"DMAdaptLabel_C",DMAdaptLabel_Plex);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

PETSC_INTERN PetscErrorCode DMClone_Plex(DM dm, DM *newdm)
{
  DM_Plex        *mesh = (DM_Plex *) dm->data;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  mesh->refct++;
  (*newdm)->data = mesh;
  ierr = PetscObjectChangeTypeName((PetscObject) *newdm, DMPLEX);CHKERRQ(ierr);
  ierr = DMInitialize_Plex(*newdm);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

/*MC
  DMPLEX = "plex" - A DM object that encapsulates an unstructured mesh, or CW Complex, which can be expressed using a Hasse Diagram.
                    In the local representation, Vecs contain all unknowns in the interior and shared boundary. This is
                    specified by a PetscSection object. Ownership in the global representation is determined by
                    ownership of the underlying DMPlex points. This is specified by another PetscSection object.

  Level: intermediate

.seealso: DMType, DMPlexCreate(), DMCreate(), DMSetType()
M*/

PETSC_EXTERN PetscErrorCode DMCreate_Plex(DM dm)
{
  DM_Plex        *mesh;
  PetscInt       unit, d;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  PetscValidHeaderSpecific(dm, DM_CLASSID, 1);
  ierr     = PetscNewLog(dm,&mesh);CHKERRQ(ierr);
  dm->dim  = 0;
  dm->data = mesh;

  mesh->refct             = 1;
  ierr                    = PetscSectionCreate(PetscObjectComm((PetscObject)dm), &mesh->coneSection);CHKERRQ(ierr);
  mesh->maxConeSize       = 0;
  mesh->cones             = NULL;
  mesh->coneOrientations  = NULL;
  ierr                    = PetscSectionCreate(PetscObjectComm((PetscObject)dm), &mesh->supportSection);CHKERRQ(ierr);
  mesh->maxSupportSize    = 0;
  mesh->supports          = NULL;
  mesh->refinementUniform = PETSC_TRUE;
  mesh->refinementLimit   = -1.0;

  mesh->facesTmp = NULL;

  mesh->tetgenOpts   = NULL;
  mesh->triangleOpts = NULL;
  ierr = PetscPartitionerCreate(PetscObjectComm((PetscObject)dm), &mesh->partitioner);CHKERRQ(ierr);
  ierr = PetscPartitionerSetTypeFromOptions_Internal(mesh->partitioner);CHKERRQ(ierr);
  mesh->remeshBd     = PETSC_FALSE;

  mesh->subpointMap = NULL;

  for (unit = 0; unit < NUM_PETSC_UNITS; ++unit) mesh->scale[unit] = 1.0;

  mesh->regularRefinement   = PETSC_FALSE;
  mesh->depthState          = -1;
  mesh->globalVertexNumbers = NULL;
  mesh->globalCellNumbers   = NULL;
  mesh->anchorSection       = NULL;
  mesh->anchorIS            = NULL;
  mesh->createanchors       = NULL;
  mesh->computeanchormatrix = NULL;
  mesh->parentSection       = NULL;
  mesh->parents             = NULL;
  mesh->childIDs            = NULL;
  mesh->childSection        = NULL;
  mesh->children            = NULL;
  mesh->referenceTree       = NULL;
  mesh->getchildsymmetry    = NULL;
  for (d = 0; d < 8; ++d) mesh->hybridPointMax[d] = PETSC_DETERMINE;
  mesh->vtkCellHeight       = 0;
  mesh->useCone             = PETSC_FALSE;
  mesh->useClosure          = PETSC_TRUE;
  mesh->useAnchors          = PETSC_FALSE;

  mesh->maxProjectionHeight = 0;

  mesh->printSetValues = PETSC_FALSE;
  mesh->printFEM       = 0;
  mesh->printTol       = 1.0e-10;

  ierr = DMInitialize_Plex(dm);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

/*@
  DMPlexCreate - Creates a DMPlex object, which encapsulates an unstructured mesh, or CW complex, which can be expressed using a Hasse Diagram.

  Collective on MPI_Comm

  Input Parameter:
. comm - The communicator for the DMPlex object

  Output Parameter:
. mesh  - The DMPlex object

  Level: beginner

.keywords: DMPlex, create
@*/
PetscErrorCode DMPlexCreate(MPI_Comm comm, DM *mesh)
{
  PetscErrorCode ierr;

  PetscFunctionBegin;
  PetscValidPointer(mesh,2);
  ierr = DMCreate(comm, mesh);CHKERRQ(ierr);
  ierr = DMSetType(*mesh, DMPLEX);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

/*
  This takes as input the common mesh generator output, a list of the vertices for each cell, but vertex numbers are global and an SF is built for them
*/
static PetscErrorCode DMPlexBuildFromCellList_Parallel_Private(DM dm, PetscInt numCells, PetscInt numVertices, PetscInt numCorners, const int cells[], PetscSF *sfVert)
{
  PetscSF         sfPoint;
  PetscLayout     vLayout;
  PetscHashI      vhash;
  PetscSFNode    *remoteVerticesAdj, *vertexLocal, *vertexOwner, *remoteVertex;
  const PetscInt *vrange;
  PetscInt        numVerticesAdj, off, *verticesAdj, numVerticesGhost = 0, *localVertex, *cone, c, p, v, g;
  PETSC_UNUSED PetscHashIIter ret, iter;
  PetscMPIInt     rank, size;
  PetscErrorCode  ierr;

  PetscFunctionBegin;
  ierr = MPI_Comm_rank(PetscObjectComm((PetscObject) dm), &rank);CHKERRQ(ierr);
  ierr = MPI_Comm_size(PetscObjectComm((PetscObject) dm), &size);CHKERRQ(ierr);
  /* Partition vertices */
  ierr = PetscLayoutCreate(PetscObjectComm((PetscObject) dm), &vLayout);CHKERRQ(ierr);
  ierr = PetscLayoutSetLocalSize(vLayout, numVertices);CHKERRQ(ierr);
  ierr = PetscLayoutSetBlockSize(vLayout, 1);CHKERRQ(ierr);
  ierr = PetscLayoutSetUp(vLayout);CHKERRQ(ierr);
  ierr = PetscLayoutGetRanges(vLayout, &vrange);CHKERRQ(ierr);
  /* Count vertices and map them to procs */
  PetscHashICreate(vhash);
  for (c = 0; c < numCells; ++c) {
    for (p = 0; p < numCorners; ++p) {
      PetscHashIPut(vhash, cells[c*numCorners+p], ret, iter);
    }
  }
  PetscHashISize(vhash, numVerticesAdj);
  ierr = PetscMalloc1(numVerticesAdj, &verticesAdj);CHKERRQ(ierr);
  off = 0; ierr = PetscHashIGetKeys(vhash, &off, verticesAdj);CHKERRQ(ierr);
  if (off != numVerticesAdj) SETERRQ2(PETSC_COMM_SELF, PETSC_ERR_ARG_WRONG, "Invalid number of local vertices %D should be %D", off, numVerticesAdj);
  ierr = PetscSortInt(numVerticesAdj, verticesAdj);CHKERRQ(ierr);
  ierr = PetscMalloc1(numVerticesAdj, &remoteVerticesAdj);CHKERRQ(ierr);
  for (v = 0; v < numVerticesAdj; ++v) {
    const PetscInt gv = verticesAdj[v];
    PetscInt       vrank;

    ierr = PetscFindInt(gv, size+1, vrange, &vrank);CHKERRQ(ierr);
    vrank = vrank < 0 ? -(vrank+2) : vrank;
    remoteVerticesAdj[v].index = gv - vrange[vrank];
    remoteVerticesAdj[v].rank  = vrank;
  }
  /* Create cones */
  ierr = DMPlexSetChart(dm, 0, numCells+numVerticesAdj);CHKERRQ(ierr);
  for (c = 0; c < numCells; ++c) {ierr = DMPlexSetConeSize(dm, c, numCorners);CHKERRQ(ierr);}
  ierr = DMSetUp(dm);CHKERRQ(ierr);
  ierr = DMGetWorkArray(dm, numCorners, PETSC_INT, &cone);CHKERRQ(ierr);
  for (c = 0; c < numCells; ++c) {
    for (p = 0; p < numCorners; ++p) {
      const PetscInt gv = cells[c*numCorners+p];
      PetscInt       lv;

      ierr = PetscFindInt(gv, numVerticesAdj, verticesAdj, &lv);CHKERRQ(ierr);
      if (lv < 0) SETERRQ1(PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Could not find global vertex %D in local connectivity", gv);
      cone[p] = lv+numCells;
    }
    ierr = DMPlexSetCone(dm, c, cone);CHKERRQ(ierr);
  }
  ierr = DMRestoreWorkArray(dm, numCorners, PETSC_INT, &cone);CHKERRQ(ierr);
  /* Create SF for vertices */
  ierr = PetscSFCreate(PetscObjectComm((PetscObject)dm), sfVert);CHKERRQ(ierr);
  ierr = PetscObjectSetName((PetscObject) *sfVert, "Vertex Ownership SF");CHKERRQ(ierr);
  ierr = PetscSFSetFromOptions(*sfVert);CHKERRQ(ierr);
  ierr = PetscSFSetGraph(*sfVert, numVertices, numVerticesAdj, NULL, PETSC_OWN_POINTER, remoteVerticesAdj, PETSC_OWN_POINTER);CHKERRQ(ierr);
  ierr = PetscFree(verticesAdj);CHKERRQ(ierr);
  /* Build pointSF */
  ierr = PetscMalloc2(numVerticesAdj, &vertexLocal, numVertices, &vertexOwner);CHKERRQ(ierr);
  for (v = 0; v < numVerticesAdj; ++v) {vertexLocal[v].index = v+numCells; vertexLocal[v].rank = rank;}
  for (v = 0; v < numVertices;    ++v) {vertexOwner[v].index = -1;         vertexOwner[v].rank = -1;}
  ierr = PetscSFReduceBegin(*sfVert, MPI_2INT, vertexLocal, vertexOwner, MPI_MAXLOC);CHKERRQ(ierr);
  ierr = PetscSFReduceEnd(*sfVert, MPI_2INT, vertexLocal, vertexOwner, MPI_MAXLOC);CHKERRQ(ierr);
  for (v = 0; v < numVertices;    ++v) if (vertexOwner[v].rank < 0) SETERRQ2(PETSC_COMM_SELF, PETSC_ERR_ARG_WRONG, "Global vertex %d on rank %d was unclaimed", v + vrange[rank], rank);
  ierr = PetscSFBcastBegin(*sfVert, MPI_2INT, vertexOwner, vertexLocal);CHKERRQ(ierr);
  ierr = PetscSFBcastEnd(*sfVert, MPI_2INT, vertexOwner, vertexLocal);CHKERRQ(ierr);
  for (v = 0; v < numVerticesAdj; ++v) if (vertexLocal[v].rank != rank) ++numVerticesGhost;
  ierr = PetscMalloc1(numVerticesGhost, &localVertex);CHKERRQ(ierr);
  ierr = PetscMalloc1(numVerticesGhost, &remoteVertex);CHKERRQ(ierr);
  for (v = 0, g = 0; v < numVerticesAdj; ++v) {
    if (vertexLocal[v].rank != rank) {
      localVertex[g]        = v+numCells;
      remoteVertex[g].index = vertexLocal[v].index;
      remoteVertex[g].rank  = vertexLocal[v].rank;
      ++g;
    }
  }
  ierr = PetscFree2(vertexLocal, vertexOwner);CHKERRQ(ierr);
  if (g != numVerticesGhost) SETERRQ2(PETSC_COMM_SELF, PETSC_ERR_PLIB, "Invalid number of vertex ghosts %D should be %D", g, numVerticesGhost);
  ierr = DMGetPointSF(dm, &sfPoint);CHKERRQ(ierr);
  ierr = PetscObjectSetName((PetscObject) sfPoint, "point SF");CHKERRQ(ierr);
  ierr = PetscSFSetGraph(sfPoint, numCells+numVerticesAdj, numVerticesGhost, localVertex, PETSC_OWN_POINTER, remoteVertex, PETSC_OWN_POINTER);CHKERRQ(ierr);
  ierr = PetscLayoutDestroy(&vLayout);CHKERRQ(ierr);
  PetscHashIDestroy(vhash);
  /* Fill in the rest of the topology structure */
  ierr = DMPlexSymmetrize(dm);CHKERRQ(ierr);
  ierr = DMPlexStratify(dm);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

/*
  This takes as input the coordinates for each owned vertex
*/
static PetscErrorCode DMPlexBuildCoordinates_Parallel_Private(DM dm, PetscInt spaceDim, PetscInt numCells, PetscInt numV, PetscSF sfVert, const PetscReal vertexCoords[])
{
  PetscSection   coordSection;
  Vec            coordinates;
  PetscScalar   *coords;
  PetscInt       numVertices, numVerticesAdj, coordSize, v;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  ierr = PetscSFGetGraph(sfVert, &numVertices, &numVerticesAdj, NULL, NULL);CHKERRQ(ierr);
  ierr = DMGetCoordinateSection(dm, &coordSection);CHKERRQ(ierr);
  ierr = PetscSectionSetNumFields(coordSection, 1);CHKERRQ(ierr);
  ierr = PetscSectionSetFieldComponents(coordSection, 0, spaceDim);CHKERRQ(ierr);
  ierr = PetscSectionSetChart(coordSection, numCells, numCells + numVerticesAdj);CHKERRQ(ierr);
  for (v = numCells; v < numCells+numVerticesAdj; ++v) {
    ierr = PetscSectionSetDof(coordSection, v, spaceDim);CHKERRQ(ierr);
    ierr = PetscSectionSetFieldDof(coordSection, v, 0, spaceDim);CHKERRQ(ierr);
  }
  ierr = PetscSectionSetUp(coordSection);CHKERRQ(ierr);
  ierr = PetscSectionGetStorageSize(coordSection, &coordSize);CHKERRQ(ierr);
  ierr = VecCreate(PetscObjectComm((PetscObject)dm), &coordinates);CHKERRQ(ierr);
  ierr = VecSetBlockSize(coordinates, spaceDim);CHKERRQ(ierr);
  ierr = PetscObjectSetName((PetscObject) coordinates, "coordinates");CHKERRQ(ierr);
  ierr = VecSetSizes(coordinates, coordSize, PETSC_DETERMINE);CHKERRQ(ierr);
  ierr = VecSetType(coordinates,VECSTANDARD);CHKERRQ(ierr);
  ierr = VecGetArray(coordinates, &coords);CHKERRQ(ierr);
  {
    MPI_Datatype coordtype;

    /* Need a temp buffer for coords if we have complex/single */
    ierr = MPI_Type_contiguous(spaceDim, MPIU_SCALAR, &coordtype);CHKERRQ(ierr);
    ierr = MPI_Type_commit(&coordtype);CHKERRQ(ierr);
#if defined(PETSC_USE_COMPLEX)
    {
    PetscScalar *svertexCoords;
    PetscInt    i;
    ierr = PetscMalloc1(numV*spaceDim,&svertexCoords);CHKERRQ(ierr);
    for (i=0; i<numV*spaceDim; i++) svertexCoords[i] = vertexCoords[i];
    ierr = PetscSFBcastBegin(sfVert, coordtype, svertexCoords, coords);CHKERRQ(ierr);
    ierr = PetscSFBcastEnd(sfVert, coordtype, svertexCoords, coords);CHKERRQ(ierr);
    ierr = PetscFree(svertexCoords);CHKERRQ(ierr);
    }
#else
    ierr = PetscSFBcastBegin(sfVert, coordtype, vertexCoords, coords);CHKERRQ(ierr);
    ierr = PetscSFBcastEnd(sfVert, coordtype, vertexCoords, coords);CHKERRQ(ierr);
#endif
    ierr = MPI_Type_free(&coordtype);CHKERRQ(ierr);
  }
  ierr = VecRestoreArray(coordinates, &coords);CHKERRQ(ierr);
  ierr = DMSetCoordinatesLocal(dm, coordinates);CHKERRQ(ierr);
  ierr = VecDestroy(&coordinates);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

/*@C
  DMPlexCreateFromCellListParallel - This takes as input common mesh generator output, a list of the vertices for each cell, and produces a DM

  Input Parameters:
+ comm - The communicator
. dim - The topological dimension of the mesh
. numCells - The number of cells owned by this process
. numVertices - The number of vertices owned by this process
. numCorners - The number of vertices for each cell
. interpolate - Flag indicating that intermediate mesh entities (faces, edges) should be created automatically
. cells - An array of numCells*numCorners numbers, the global vertex numbers for each cell
. spaceDim - The spatial dimension used for coordinates
- vertexCoords - An array of numVertices*spaceDim numbers, the coordinates of each vertex

  Output Parameter:
+ dm - The DM
- vertexSF - Optional, SF describing complete vertex ownership

  Note: Two triangles sharing a face
$
$        2
$      / | \
$     /  |  \
$    /   |   \
$   0  0 | 1  3
$    \   |   /
$     \  |  /
$      \ | /
$        1
would have input
$  numCells = 2, numVertices = 4
$  cells = [0 1 2  1 3 2]
$
which would result in the DMPlex
$
$        4
$      / | \
$     /  |  \
$    /   |   \
$   2  0 | 1  5
$    \   |   /
$     \  |  /
$      \ | /
$        3

  Level: beginner

.seealso: DMPlexCreateFromCellList(), DMPlexCreateFromDAG(), DMPlexCreate()
@*/
PetscErrorCode DMPlexCreateFromCellListParallel(MPI_Comm comm, PetscInt dim, PetscInt numCells, PetscInt numVertices, PetscInt numCorners, PetscBool interpolate, const int cells[], PetscInt spaceDim, const PetscReal vertexCoords[], PetscSF *vertexSF, DM *dm)
{
  PetscSF        sfVert;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  ierr = DMCreate(comm, dm);CHKERRQ(ierr);
  ierr = DMSetType(*dm, DMPLEX);CHKERRQ(ierr);
  PetscValidLogicalCollectiveInt(*dm, dim, 2);
  PetscValidLogicalCollectiveInt(*dm, spaceDim, 8);
  ierr = DMSetDimension(*dm, dim);CHKERRQ(ierr);
  ierr = DMPlexBuildFromCellList_Parallel_Private(*dm, numCells, numVertices, numCorners, cells, &sfVert);CHKERRQ(ierr);
  if (interpolate) {
    DM idm = NULL;

    ierr = DMPlexInterpolate(*dm, &idm);CHKERRQ(ierr);
    ierr = DMDestroy(dm);CHKERRQ(ierr);
    *dm  = idm;
  }
  ierr = DMPlexBuildCoordinates_Parallel_Private(*dm, spaceDim, numCells, numVertices,sfVert, vertexCoords);CHKERRQ(ierr);
  if (vertexSF) *vertexSF = sfVert;
  else {ierr = PetscSFDestroy(&sfVert);CHKERRQ(ierr);}
  PetscFunctionReturn(0);
}

/*
  This takes as input the common mesh generator output, a list of the vertices for each cell
*/
static PetscErrorCode DMPlexBuildFromCellList_Private(DM dm, PetscInt numCells, PetscInt numVertices, PetscInt numCorners, const int cells[])
{
  PetscInt      *cone, c, p;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  ierr = DMPlexSetChart(dm, 0, numCells+numVertices);CHKERRQ(ierr);
  for (c = 0; c < numCells; ++c) {
    ierr = DMPlexSetConeSize(dm, c, numCorners);CHKERRQ(ierr);
  }
  ierr = DMSetUp(dm);CHKERRQ(ierr);
  ierr = DMGetWorkArray(dm, numCorners, PETSC_INT, &cone);CHKERRQ(ierr);
  for (c = 0; c < numCells; ++c) {
    for (p = 0; p < numCorners; ++p) {
      cone[p] = cells[c*numCorners+p]+numCells;
    }
    ierr = DMPlexSetCone(dm, c, cone);CHKERRQ(ierr);
  }
  ierr = DMRestoreWorkArray(dm, numCorners, PETSC_INT, &cone);CHKERRQ(ierr);
  ierr = DMPlexSymmetrize(dm);CHKERRQ(ierr);
  ierr = DMPlexStratify(dm);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

/*
  This takes as input the coordinates for each vertex
*/
static PetscErrorCode DMPlexBuildCoordinates_Private(DM dm, PetscInt spaceDim, PetscInt numCells, PetscInt numVertices, const double vertexCoords[])
{
  PetscSection   coordSection;
  Vec            coordinates;
  DM             cdm;
  PetscScalar   *coords;
  PetscInt       v, d;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  ierr = DMGetCoordinateSection(dm, &coordSection);CHKERRQ(ierr);
  ierr = PetscSectionSetNumFields(coordSection, 1);CHKERRQ(ierr);
  ierr = PetscSectionSetFieldComponents(coordSection, 0, spaceDim);CHKERRQ(ierr);
  ierr = PetscSectionSetChart(coordSection, numCells, numCells + numVertices);CHKERRQ(ierr);
  for (v = numCells; v < numCells+numVertices; ++v) {
    ierr = PetscSectionSetDof(coordSection, v, spaceDim);CHKERRQ(ierr);
    ierr = PetscSectionSetFieldDof(coordSection, v, 0, spaceDim);CHKERRQ(ierr);
  }
  ierr = PetscSectionSetUp(coordSection);CHKERRQ(ierr);

  ierr = DMGetCoordinateDM(dm, &cdm);CHKERRQ(ierr);
  ierr = DMCreateLocalVector(cdm, &coordinates);CHKERRQ(ierr);
  ierr = VecSetBlockSize(coordinates, spaceDim);CHKERRQ(ierr);
  ierr = PetscObjectSetName((PetscObject) coordinates, "coordinates");CHKERRQ(ierr);
  ierr = VecGetArray(coordinates, &coords);CHKERRQ(ierr);
  for (v = 0; v < numVertices; ++v) {
    for (d = 0; d < spaceDim; ++d) {
      coords[v*spaceDim+d] = vertexCoords[v*spaceDim+d];
    }
  }
  ierr = VecRestoreArray(coordinates, &coords);CHKERRQ(ierr);
  ierr = DMSetCoordinatesLocal(dm, coordinates);CHKERRQ(ierr);
  ierr = VecDestroy(&coordinates);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

/*@C
  DMPlexCreateFromCellList - This takes as input common mesh generator output, a list of the vertices for each cell, and produces a DM

  Input Parameters:
+ comm - The communicator
. dim - The topological dimension of the mesh
. numCells - The number of cells
. numVertices - The number of vertices
. numCorners - The number of vertices for each cell
. interpolate - Flag indicating that intermediate mesh entities (faces, edges) should be created automatically
. cells - An array of numCells*numCorners numbers, the vertices for each cell
. spaceDim - The spatial dimension used for coordinates
- vertexCoords - An array of numVertices*spaceDim numbers, the coordinates of each vertex

  Output Parameter:
. dm - The DM

  Note: Two triangles sharing a face
$
$        2
$      / | \
$     /  |  \
$    /   |   \
$   0  0 | 1  3
$    \   |   /
$     \  |  /
$      \ | /
$        1
would have input
$  numCells = 2, numVertices = 4
$  cells = [0 1 2  1 3 2]
$
which would result in the DMPlex
$
$        4
$      / | \
$     /  |  \
$    /   |   \
$   2  0 | 1  5
$    \   |   /
$     \  |  /
$      \ | /
$        3

  Level: beginner

.seealso: DMPlexCreateFromDAG(), DMPlexCreate()
@*/
PetscErrorCode DMPlexCreateFromCellList(MPI_Comm comm, PetscInt dim, PetscInt numCells, PetscInt numVertices, PetscInt numCorners, PetscBool interpolate, const int cells[], PetscInt spaceDim, const double vertexCoords[], DM *dm)
{
  PetscErrorCode ierr;

  PetscFunctionBegin;
  ierr = DMCreate(comm, dm);CHKERRQ(ierr);
  ierr = DMSetType(*dm, DMPLEX);CHKERRQ(ierr);
  ierr = DMSetDimension(*dm, dim);CHKERRQ(ierr);
  ierr = DMPlexBuildFromCellList_Private(*dm, numCells, numVertices, numCorners, cells);CHKERRQ(ierr);
  if (interpolate) {
    DM idm = NULL;

    ierr = DMPlexInterpolate(*dm, &idm);CHKERRQ(ierr);
    ierr = DMDestroy(dm);CHKERRQ(ierr);
    *dm  = idm;
  }
  ierr = DMPlexBuildCoordinates_Private(*dm, spaceDim, numCells, numVertices, vertexCoords);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

/*@
  DMPlexCreateFromDAG - This takes as input the adjacency-list representation of the Directed Acyclic Graph (Hasse Diagram) encoding a mesh, and produces a DM

  Input Parameters:
+ dm - The empty DM object, usually from DMCreate() and DMSetDimension()
. depth - The depth of the DAG
. numPoints - The number of points at each depth
. coneSize - The cone size of each point
. cones - The concatenation of the cone points for each point, the cone list must be oriented correctly for each point
. coneOrientations - The orientation of each cone point
- vertexCoords - An array of numVertices*dim numbers, the coordinates of each vertex

  Output Parameter:
. dm - The DM

  Note: Two triangles sharing a face would have input
$  depth = 1, numPoints = [4 2], coneSize = [3 3 0 0 0 0]
$  cones = [2 3 4  3 5 4], coneOrientations = [0 0 0  0 0 0]
$ vertexCoords = [-1.0 0.0  0.0 -1.0  0.0 1.0  1.0 0.0]
$
which would result in the DMPlex
$
$        4
$      / | \
$     /  |  \
$    /   |   \
$   2  0 | 1  5
$    \   |   /
$     \  |  /
$      \ | /
$        3
$
$ Notice that all points are numbered consecutively, unlikely DMPlexCreateFromCellList()

  Level: advanced

.seealso: DMPlexCreateFromCellList(), DMPlexCreate()
@*/
PetscErrorCode DMPlexCreateFromDAG(DM dm, PetscInt depth, const PetscInt numPoints[], const PetscInt coneSize[], const PetscInt cones[], const PetscInt coneOrientations[], const PetscScalar vertexCoords[])
{
  Vec            coordinates;
  PetscSection   coordSection;
  PetscScalar    *coords;
  PetscInt       coordSize, firstVertex = -1, pStart = 0, pEnd = 0, p, v, dim, dimEmbed, d, off;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  ierr = DMGetDimension(dm, &dim);CHKERRQ(ierr);
  ierr = DMGetCoordinateDim(dm, &dimEmbed);CHKERRQ(ierr);
  if (dimEmbed < dim) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Embedding dimension %d cannot be less than intrinsic dimension %d",dimEmbed,dim);
  for (d = 0; d <= depth; ++d) pEnd += numPoints[d];
  ierr = DMPlexSetChart(dm, pStart, pEnd);CHKERRQ(ierr);
  for (p = pStart; p < pEnd; ++p) {
    ierr = DMPlexSetConeSize(dm, p, coneSize[p-pStart]);CHKERRQ(ierr);
    if (firstVertex < 0 && !coneSize[p - pStart]) {
      firstVertex = p - pStart;
    }
  }
  if (firstVertex < 0 && numPoints[0]) SETERRQ1(PETSC_COMM_SELF,PETSC_ERR_ARG_WRONG,"Expected %d vertices but could not find any", numPoints[0]);
  ierr = DMSetUp(dm);CHKERRQ(ierr); /* Allocate space for cones */
  for (p = pStart, off = 0; p < pEnd; off += coneSize[p-pStart], ++p) {
    ierr = DMPlexSetCone(dm, p, &cones[off]);CHKERRQ(ierr);
    ierr = DMPlexSetConeOrientation(dm, p, &coneOrientations[off]);CHKERRQ(ierr);
  }
  ierr = DMPlexSymmetrize(dm);CHKERRQ(ierr);
  ierr = DMPlexStratify(dm);CHKERRQ(ierr);
  /* Build coordinates */
  ierr = DMGetCoordinateSection(dm, &coordSection);CHKERRQ(ierr);
  ierr = PetscSectionSetNumFields(coordSection, 1);CHKERRQ(ierr);
  ierr = PetscSectionSetFieldComponents(coordSection, 0, dimEmbed);CHKERRQ(ierr);
  ierr = PetscSectionSetChart(coordSection, firstVertex, firstVertex+numPoints[0]);CHKERRQ(ierr);
  for (v = firstVertex; v < firstVertex+numPoints[0]; ++v) {
    ierr = PetscSectionSetDof(coordSection, v, dimEmbed);CHKERRQ(ierr);
    ierr = PetscSectionSetFieldDof(coordSection, v, 0, dimEmbed);CHKERRQ(ierr);
  }
  ierr = PetscSectionSetUp(coordSection);CHKERRQ(ierr);
  ierr = PetscSectionGetStorageSize(coordSection, &coordSize);CHKERRQ(ierr);
  ierr = VecCreate(PETSC_COMM_SELF, &coordinates);CHKERRQ(ierr);
  ierr = PetscObjectSetName((PetscObject) coordinates, "coordinates");CHKERRQ(ierr);
  ierr = VecSetSizes(coordinates, coordSize, PETSC_DETERMINE);CHKERRQ(ierr);
  ierr = VecSetBlockSize(coordinates, dimEmbed);CHKERRQ(ierr);
  ierr = VecSetType(coordinates,VECSTANDARD);CHKERRQ(ierr);
  ierr = VecGetArray(coordinates, &coords);CHKERRQ(ierr);
  for (v = 0; v < numPoints[0]; ++v) {
    PetscInt off;

    ierr = PetscSectionGetOffset(coordSection, v+firstVertex, &off);CHKERRQ(ierr);
    for (d = 0; d < dimEmbed; ++d) {
      coords[off+d] = vertexCoords[v*dimEmbed+d];
    }
  }
  ierr = VecRestoreArray(coordinates, &coords);CHKERRQ(ierr);
  ierr = DMSetCoordinatesLocal(dm, coordinates);CHKERRQ(ierr);
  ierr = VecDestroy(&coordinates);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

/*@C
  DMPlexCreateFromFile - This takes a filename and produces a DM

  Input Parameters:
+ comm - The communicator
. filename - A file name
- interpolate - Flag to create intermediate mesh pieces (edges, faces)

  Output Parameter:
. dm - The DM

  Level: beginner

.seealso: DMPlexCreateFromDAG(), DMPlexCreateFromCellList(), DMPlexCreate()
@*/
PetscErrorCode DMPlexCreateFromFile(MPI_Comm comm, const char filename[], PetscBool interpolate, DM *dm)
{
  const char    *extGmsh   = ".msh";
  const char    *extCGNS   = ".cgns";
  const char    *extExodus = ".exo";
  const char    *extFluent = ".cas";
  const char    *extHDF5   = ".h5";
  const char    *extMed    = ".med";
  size_t         len;
  PetscBool      isGmsh, isCGNS, isExodus, isFluent, isHDF5, isMed;
  PetscMPIInt    rank;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  PetscValidPointer(filename, 2);
  PetscValidPointer(dm, 4);
  ierr = MPI_Comm_rank(comm, &rank);CHKERRQ(ierr);
  ierr = PetscStrlen(filename, &len);CHKERRQ(ierr);
  if (!len) SETERRQ(comm, PETSC_ERR_ARG_WRONG, "Filename must be a valid path");
  ierr = PetscStrncmp(&filename[PetscMax(0,len-4)], extGmsh,   4, &isGmsh);CHKERRQ(ierr);
  ierr = PetscStrncmp(&filename[PetscMax(0,len-5)], extCGNS,   5, &isCGNS);CHKERRQ(ierr);
  ierr = PetscStrncmp(&filename[PetscMax(0,len-4)], extExodus, 4, &isExodus);CHKERRQ(ierr);
  ierr = PetscStrncmp(&filename[PetscMax(0,len-4)], extFluent, 4, &isFluent);CHKERRQ(ierr);
  ierr = PetscStrncmp(&filename[PetscMax(0,len-3)], extHDF5,   3, &isHDF5);CHKERRQ(ierr);
  ierr = PetscStrncmp(&filename[PetscMax(0,len-4)], extMed,    4, &isMed);CHKERRQ(ierr);
  if (isGmsh) {
    ierr = DMPlexCreateGmshFromFile(comm, filename, interpolate, dm);CHKERRQ(ierr);
  } else if (isCGNS) {
    ierr = DMPlexCreateCGNSFromFile(comm, filename, interpolate, dm);CHKERRQ(ierr);
  } else if (isExodus) {
    ierr = DMPlexCreateExodusFromFile(comm, filename, interpolate, dm);CHKERRQ(ierr);
  } else if (isFluent) {
    ierr = DMPlexCreateFluentFromFile(comm, filename, interpolate, dm);CHKERRQ(ierr);
  } else if (isHDF5) {
    PetscViewer viewer;

    ierr = PetscViewerCreate(comm, &viewer);CHKERRQ(ierr);
    ierr = PetscViewerSetType(viewer, PETSCVIEWERHDF5);CHKERRQ(ierr);
    ierr = PetscViewerFileSetMode(viewer, FILE_MODE_READ);CHKERRQ(ierr);
    ierr = PetscViewerFileSetName(viewer, filename);CHKERRQ(ierr);
    ierr = DMCreate(comm, dm);CHKERRQ(ierr);
    ierr = DMSetType(*dm, DMPLEX);CHKERRQ(ierr);
    ierr = DMLoad(*dm, viewer);CHKERRQ(ierr);
    ierr = PetscViewerDestroy(&viewer);CHKERRQ(ierr);
  } else if (isMed) {
    ierr = DMPlexCreateMedFromFile(comm, filename, interpolate, dm);CHKERRQ(ierr);
  } else SETERRQ1(PETSC_COMM_SELF, PETSC_ERR_ARG_WRONG, "Cannot load file %s: unrecognized extension", filename);
  PetscFunctionReturn(0);
}

/*@
  DMPlexCreateReferenceCell - Create a DMPLEX with the appropriate FEM reference cell

  Collective on comm

  Input Parameters:
+ comm    - The communicator
. dim     - The spatial dimension
- simplex - Flag for simplex, otherwise use a tensor-product cell

  Output Parameter:
. refdm - The reference cell

  Level: intermediate

.keywords: reference cell
.seealso:
@*/
PetscErrorCode DMPlexCreateReferenceCell(MPI_Comm comm, PetscInt dim, PetscBool simplex, DM *refdm)
{
  DM             rdm;
  Vec            coords;
  PetscErrorCode ierr;

  PetscFunctionBeginUser;
  ierr = DMCreate(comm, &rdm);CHKERRQ(ierr);
  ierr = DMSetType(rdm, DMPLEX);CHKERRQ(ierr);
  ierr = DMSetDimension(rdm, dim);CHKERRQ(ierr);
  switch (dim) {
  case 0:
  {
    PetscInt    numPoints[1]        = {1};
    PetscInt    coneSize[1]         = {0};
    PetscInt    cones[1]            = {0};
    PetscInt    coneOrientations[1] = {0};
    PetscScalar vertexCoords[1]     = {0.0};

    ierr = DMPlexCreateFromDAG(rdm, 0, numPoints, coneSize, cones, coneOrientations, vertexCoords);CHKERRQ(ierr);
  }
  break;
  case 1:
  {
    PetscInt    numPoints[2]        = {2, 1};
    PetscInt    coneSize[3]         = {2, 0, 0};
    PetscInt    cones[2]            = {1, 2};
    PetscInt    coneOrientations[2] = {0, 0};
    PetscScalar vertexCoords[2]     = {-1.0,  1.0};

    ierr = DMPlexCreateFromDAG(rdm, 1, numPoints, coneSize, cones, coneOrientations, vertexCoords);CHKERRQ(ierr);
  }
  break;
  case 2:
    if (simplex) {
      PetscInt    numPoints[2]        = {3, 1};
      PetscInt    coneSize[4]         = {3, 0, 0, 0};
      PetscInt    cones[3]            = {1, 2, 3};
      PetscInt    coneOrientations[3] = {0, 0, 0};
      PetscScalar vertexCoords[6]     = {-1.0, -1.0,  1.0, -1.0,  -1.0, 1.0};

      ierr = DMPlexCreateFromDAG(rdm, 1, numPoints, coneSize, cones, coneOrientations, vertexCoords);CHKERRQ(ierr);
    } else {
      PetscInt    numPoints[2]        = {4, 1};
      PetscInt    coneSize[5]         = {4, 0, 0, 0, 0};
      PetscInt    cones[4]            = {1, 2, 3, 4};
      PetscInt    coneOrientations[4] = {0, 0, 0, 0};
      PetscScalar vertexCoords[8]     = {-1.0, -1.0,  1.0, -1.0,  1.0, 1.0,  -1.0, 1.0};

      ierr = DMPlexCreateFromDAG(rdm, 1, numPoints, coneSize, cones, coneOrientations, vertexCoords);CHKERRQ(ierr);
    }
  break;
  case 3:
    if (simplex) {
      PetscInt    numPoints[2]        = {4, 1};
      PetscInt    coneSize[5]         = {4, 0, 0, 0, 0};
      PetscInt    cones[4]            = {1, 3, 2, 4};
      PetscInt    coneOrientations[4] = {0, 0, 0, 0};
      PetscScalar vertexCoords[12]    = {-1.0, -1.0, -1.0,  1.0, -1.0, -1.0,  -1.0, 1.0, -1.0,  -1.0, -1.0, 1.0};

      ierr = DMPlexCreateFromDAG(rdm, 1, numPoints, coneSize, cones, coneOrientations, vertexCoords);CHKERRQ(ierr);
    } else {
      PetscInt    numPoints[2]        = {8, 1};
      PetscInt    coneSize[9]         = {8, 0, 0, 0, 0, 0, 0, 0, 0};
      PetscInt    cones[8]            = {1, 4, 3, 2, 5, 6, 7, 8};
      PetscInt    coneOrientations[8] = {0, 0, 0, 0, 0, 0, 0, 0};
      PetscScalar vertexCoords[24]    = {-1.0, -1.0, -1.0,  1.0, -1.0, -1.0,  1.0, 1.0, -1.0,  -1.0, 1.0, -1.0,
                                         -1.0, -1.0,  1.0,  1.0, -1.0,  1.0,  1.0, 1.0,  1.0,  -1.0, 1.0,  1.0};

      ierr = DMPlexCreateFromDAG(rdm, 1, numPoints, coneSize, cones, coneOrientations, vertexCoords);CHKERRQ(ierr);
    }
  break;
  default:
    SETERRQ1(comm, PETSC_ERR_ARG_WRONG, "Cannot create reference cell for dimension %d", dim);
  }
  *refdm = NULL;
  ierr = DMPlexInterpolate(rdm, refdm);CHKERRQ(ierr);
  if (rdm->coordinateDM) {
    DM           ncdm;
    PetscSection cs;
    PetscInt     pEnd = -1;

    ierr = DMGetDefaultSection(rdm->coordinateDM, &cs);CHKERRQ(ierr);
    if (cs) {ierr = PetscSectionGetChart(cs, NULL, &pEnd);CHKERRQ(ierr);}
    if (pEnd >= 0) {
      ierr = DMClone(rdm->coordinateDM, &ncdm);CHKERRQ(ierr);
      ierr = DMSetDefaultSection(ncdm, cs);CHKERRQ(ierr);
      ierr = DMSetCoordinateDM(*refdm, ncdm);CHKERRQ(ierr);
      ierr = DMDestroy(&ncdm);CHKERRQ(ierr);
    }
  }
  ierr = DMGetCoordinatesLocal(rdm, &coords);CHKERRQ(ierr);
  if (coords) {
    ierr = DMSetCoordinatesLocal(*refdm, coords);CHKERRQ(ierr);
  } else {
    ierr = DMGetCoordinates(rdm, &coords);CHKERRQ(ierr);
    if (coords) {ierr = DMSetCoordinates(*refdm, coords);CHKERRQ(ierr);}
  }
  ierr = DMDestroy(&rdm);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}