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