1: static char help[] = "Define a simple field over the mesh\n\n";

  3: #include <petscdmplex.h>

  7: int main(int argc, char **argv)
  8: {
  9:   DM             dm, dmDist = NULL;
 10:   Vec            u;
 11:   PetscSection   section;
 12:   PetscViewer    viewer;
 13:   PetscInt       dim = 2, numFields, numBC, i;
 14:   PetscInt       numComp[3];
 15:   PetscInt       numDof[12];
 16:   PetscInt       bcField[1];
 17:   IS             bcPointIS[1];
 18:   PetscBool      interpolate = PETSC_TRUE;

 21:   PetscInitialize(&argc, &argv, NULL, help);
 22:   PetscOptionsGetInt(NULL, "-dim", &dim, NULL);
 23:   /* Create a mesh */
 24:   DMPlexCreateBoxMesh(PETSC_COMM_WORLD, dim, interpolate, &dm);
 25:   /* Distribute mesh over processes */
 26:   DMPlexDistribute(dm, NULL, 0, NULL, &dmDist);
 27:   if (dmDist) {DMDestroy(&dm); dm = dmDist;}
 28:   /* Create a scalar field u, a vector field v, and a surface vector field w */
 29:   numFields  = 3;
 30:   numComp[0] = 1;
 31:   numComp[1] = dim;
 32:   numComp[2] = dim-1;
 33:   for (i = 0; i < numFields*(dim+1); ++i) numDof[i] = 0;
 34:   /* Let u be defined on vertices */
 35:   numDof[0*(dim+1)+0]     = 1;
 36:   /* Let v be defined on cells */
 37:   numDof[1*(dim+1)+dim]   = dim;
 38:   /* Let v be defined on faces */
 39:   numDof[2*(dim+1)+dim-1] = dim-1;
 40:   /* Setup boundary conditions */
 41:   numBC = 1;
 42:   /* Prescribe a Dirichlet condition on u on the boundary
 43:        Label "marker" is made by the mesh creation routine */
 44:   bcField[0] = 0;
 45:   DMPlexGetStratumIS(dm, "marker", 1, &bcPointIS[0]);
 46:   /* Create a PetscSection with this data layout */
 47:   DMPlexCreateSection(dm, dim, numFields, numComp, numDof, numBC, bcField, bcPointIS, NULL, &section);
 48:   ISDestroy(&bcPointIS[0]);
 49:   /* Name the Field variables */
 50:   PetscSectionSetFieldName(section, 0, "u");
 51:   PetscSectionSetFieldName(section, 1, "v");
 52:   PetscSectionSetFieldName(section, 2, "w");
 53:   PetscSectionView(section, PETSC_VIEWER_STDOUT_WORLD);
 54:   /* Tell the DM to use this data layout */
 55:   DMSetDefaultSection(dm, section);
 56:   /* Create a Vec with this layout and view it */
 57:   DMGetGlobalVector(dm, &u);
 58:   PetscViewerCreate(PETSC_COMM_WORLD, &viewer);
 59:   PetscViewerSetType(viewer, PETSCVIEWERVTK);
 60:   PetscViewerSetFormat(viewer, PETSC_VIEWER_ASCII_VTK);
 61:   PetscViewerFileSetName(viewer, "sol.vtk");
 62:   VecView(u, viewer);
 63:   PetscViewerDestroy(&viewer);
 64:   DMRestoreGlobalVector(dm, &u);
 65:   /* Cleanup */
 66:   PetscSectionDestroy(&section);
 67:   DMDestroy(&dm);
 68:   PetscFinalize();
 69:   return 0;
 70: }