DMBoundaryType#

Describes the choice for the filling of ghost cells on physical domain boundaries.

Synopsis#

typedef enum {
  DM_BOUNDARY_NONE,
  DM_BOUNDARY_GHOSTED,
  DM_BOUNDARY_MIRROR,
  DM_BOUNDARY_PERIODIC,
  DM_BOUNDARY_TWIST
} DMBoundaryType;

Values#

DM_BOUNDARY_NONE - no ghost nodes
DM_BOUNDARY_GHOSTED - ghost vertices/cells exist but aren’t filled; you can put values into them and then apply a stencil that uses those ghost locations
DM_BOUNDARY_MIRROR - the ghost value is the same as the value 1 grid point in; that is, the 0th grid point in the real mesh acts like a mirror to define the ghost point value; not yet implemented for 3d
DM_BOUNDARY_PERIODIC - ghost vertices/cells filled by the opposite edge of the domain
DM_BOUNDARY_TWIST - like periodic, only glued backwards like a Mobius strip

Notes#

This is information for the boundary of the PHYSICAL domain. It has nothing to do with boundaries between processes. That width is always determined by the stencil width; see DMDASetStencilWidth().

If the physical grid points have values 0 1 2 3 with DM_BOUNDARY_MIRROR then the local vector with ghost points has the values 1 0 1 2 3 2.

See https://scicomp.stackexchange.com/questions/5355/writing-the-poisson-equation-finite-difference-matrix-with-neumann-boundary-cond

Developer Note#

Should DM_BOUNDARY_MIRROR have the same meaning with DMDA_Q0, that is a staggered grid? In that case should the ghost point have the same value as the 0th grid point where the physical boundary serves as the mirror?