# DMBoundaryType#

Describes the choice for fill 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;


A boundary may be of type 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), or 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 .

## Developer Notes#

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?

## References#

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

DMDASetBoundaryType(), DMDACreate1d(), DMDACreate2d(), DMDACreate3d(), DMDACreate()

beginner

## Location#

include/petscdmtypes.h

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