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