static PetscErrorCode SetupSection(DM dm)
{
PetscSection s;
PetscInt vStart, vEnd, v;
PetscErrorCode ierr;
PetscFunctionBeginUser;
ierr = DMPlexGetDepthStratum(dm, 0, &vStart, &vEnd);CHKERRQ(ierr);
ierr = PetscSectionCreate(PetscObjectComm((PetscObject) dm), &s);CHKERRQ(ierr);
ierr = PetscSectionSetNumFields(s, 1);CHKERRQ(ierr);
ierr = PetscSectionSetFieldComponents(s, 0, 1);CHKERRQ(ierr);
ierr = PetscSectionSetChart(s, vStart, vEnd);CHKERRQ(ierr);
for (v = vStart; v < vEnd; ++v) {
ierr = PetscSectionSetDof(s, v, 1);CHKERRQ(ierr);
ierr = PetscSectionSetFieldDof(s, v, 0, 1);CHKERRQ(ierr);
}
ierr = PetscSectionSetUp(s);CHKERRQ(ierr);
ierr = DMSetSection(dm, s);CHKERRQ(ierr);
ierr = PetscSectionDestroy(&s);CHKERRQ(ierr);
PetscFunctionReturn(0);
}
int main(int argc, char **argv)
{
DM dm, dmDist = NULL;
Vec u;
PetscSection section;
PetscViewer viewer;
PetscInt dim = 2, numFields, numBC, i;
PetscInt numComp[3];
PetscInt numDof[12];
PetscInt bcField[1];
IS bcPointIS[1];
PetscBool interpolate = PETSC_TRUE;
PetscErrorCode ierr;
ierr = PetscInitialize(&argc, &argv, NULL,help);if (ierr) return ierr;
ierr = PetscOptionsGetInt(NULL,NULL, "-dim", &dim, NULL);CHKERRQ(ierr);
/* Create a mesh */
ierr = DMPlexCreateBoxMesh(PETSC_COMM_WORLD, dim, PETSC_TRUE, NULL, NULL, NULL, NULL, interpolate, &dm);CHKERRQ(ierr);
/* Distribute mesh over processes */
ierr = DMPlexDistribute(dm, 0, NULL, &dmDist);CHKERRQ(ierr);
if (dmDist) {ierr = DMDestroy(&dm);CHKERRQ(ierr); dm = dmDist;}
/* Create a scalar field u, a vector field v, and a surface vector field w */
numFields = 3;
numComp[0] = 1;
numComp[1] = dim;
numComp[2] = dim-1;
for (i = 0; i < numFields*(dim+1); ++i) numDof[i] = 0;
/* Let u be defined on vertices */
numDof[0*(dim+1)+0] = 1;
/* Let v be defined on cells */
numDof[1*(dim+1)+dim] = dim;
/* Let v be defined on faces */
numDof[2*(dim+1)+dim-1] = dim-1;
/* Setup boundary conditions */
numBC = 1;
/* Prescribe a Dirichlet condition on u on the boundary
Label "marker" is made by the mesh creation routine */
bcField[0] = 0;
ierr = DMGetStratumIS(dm, "marker", 1, &bcPointIS[0]);CHKERRQ(ierr);
/* Create a PetscSection with this data layout */
ierr = DMSetNumFields(dm, numFields);CHKERRQ(ierr);
ierr = DMPlexCreateSection(dm, NULL, numComp, numDof, numBC, bcField, NULL, bcPointIS, NULL, §ion);CHKERRQ(ierr);
ierr = ISDestroy(&bcPointIS[0]);CHKERRQ(ierr);
/* Name the Field variables */
ierr = PetscSectionSetFieldName(section, 0, "u");CHKERRQ(ierr);
ierr = PetscSectionSetFieldName(section, 1, "v");CHKERRQ(ierr);
ierr = PetscSectionSetFieldName(section, 2, "w");CHKERRQ(ierr);
ierr = PetscSectionView(section, PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
/* Tell the DM to use this data layout */
ierr = DMSetSection(dm, section);CHKERRQ(ierr);
/* Create a Vec with this layout and view it */
ierr = DMGetGlobalVector(dm, &u);CHKERRQ(ierr);
ierr = PetscViewerCreate(PETSC_COMM_WORLD, &viewer);CHKERRQ(ierr);
ierr = PetscViewerSetType(viewer, PETSCVIEWERVTK);CHKERRQ(ierr);
ierr = PetscViewerPushFormat(viewer, PETSC_VIEWER_ASCII_VTK);CHKERRQ(ierr);
ierr = PetscViewerFileSetName(viewer, "sol.vtk");CHKERRQ(ierr);
ierr = VecView(u, viewer);CHKERRQ(ierr);
ierr = PetscViewerDestroy(&viewer);CHKERRQ(ierr);
ierr = DMRestoreGlobalVector(dm, &u);CHKERRQ(ierr);
/* Cleanup */
ierr = PetscSectionDestroy(§ion);CHKERRQ(ierr);
ierr = DMDestroy(&dm);CHKERRQ(ierr);
ierr = PetscFinalize();
return ierr;
}
//! Help PETSc identify the coarser DM dmc given the fine DM dmf
PetscErrorCode libmesh_petsc_DMCoarsen(DM dmf, MPI_Comm /*comm*/, DM * dmc)
{
libmesh_assert(dmc);
libmesh_assert(dmf);
PetscErrorCode ierr;
// Extract our context from the incoming dmf
void * ctx_f = nullptr;
ierr = DMShellGetContext(dmf, &ctx_f);LIBMESH_CHKERR(ierr);
libmesh_assert(ctx_f);
PetscDMContext * p_ctx = static_cast<PetscDMContext*>(ctx_f);
// First, ensure that there exists a coarse DM that we want to
// set. There ought to be as we created it while walking the
// hierarchy.
libmesh_assert(p_ctx->coarser_dm);
libmesh_assert(*(p_ctx->coarser_dm));
// In situations using fieldsplit we need to (potentially)
// provide a coarser DM which only has the relevant subfields in
// it. Since we create global DMs for each mesh level, we need
// to extract the section from the DM, and check the number of
// fields. When less than all the fields are used, we need to
// create the proper subsections.
// Get the number of fields and their names from the incomming
// fine DM and the global reference DM
PetscInt nfieldsf, nfieldsg;
char ** fieldnamesf;
char ** fieldnamesg;
libmesh_assert(p_ctx->global_dm);
DM * globaldm = p_ctx->global_dm;
ierr = DMCreateFieldIS(dmf, &nfieldsf, &fieldnamesf, nullptr);
LIBMESH_CHKERR(ierr);
ierr = DMCreateFieldIS(*globaldm, &nfieldsg, &fieldnamesg, nullptr);
LIBMESH_CHKERR(ierr);
// If the probed number of fields is less than the number of
// global fields, this amounts to PETSc 'indicating' to us we
// are doing FS. So, we must create subsections for the coarser
// DMs.
if ( nfieldsf < nfieldsg )
{
PetscSection section;
PetscSection subsection;
std::vector<PetscInt> subfields(nfieldsf); // extracted fields
// First, get the section from the coarse DM
#if PETSC_VERSION_LESS_THAN(3,10,0)
ierr = DMGetDefaultSection(*(p_ctx->coarser_dm), §ion);
#else
ierr = DMGetSection(*(p_ctx->coarser_dm), §ion);
#endif
LIBMESH_CHKERR(ierr);
// Now, match fine grid DM field names to their global DM
// counterparts. Since PETSc can internally reassign field
// numbering under a fieldsplit, we must extract
// subsections via the field names. This is admittedly
// gross, but c'est la vie.
for (int i = 0; i < nfieldsf ; i++)
{
for (int j = 0; j < nfieldsg ;j++)
if ( strcmp( fieldnamesg[j], fieldnamesf[i] ) == 0 )
subfields[i] = j;
}
// Next, for the found fields we now make a subsection and set it for the coarser DM
ierr = PetscSectionCreateSubsection(section, nfieldsf, subfields.data(), &subsection);
LIBMESH_CHKERR(ierr);
#if PETSC_VERSION_LESS_THAN(3,10,0)
ierr = DMSetDefaultSection(*(p_ctx->coarser_dm) , subsection);
#else
ierr = DMSetSection(*(p_ctx->coarser_dm) , subsection);
#endif
LIBMESH_CHKERR(ierr);
ierr = PetscSectionDestroy(&subsection);
LIBMESH_CHKERR(ierr);
}
// Finally, set the coarser DM
*(dmc) = *(p_ctx->coarser_dm);
return 0;
}
