hi
I have a distributed DMPlex representing a finite volume mesh, and first
I want to check if I understand the way the indexing of ghost cells
works, based on my experiments.
As I understand it, there are two types of ghost cells:
1) those created by DMPlexDistribute() (which I call with overlap = 1),
representing the cells over the edge of the processor partition boundary
2) those created by DMPlexConstructGhostCells(), which I call to add
ghost cells on the physical boundary of the mesh (using a DMLabel), for
applying boundary conditions
The type 1 'partition' ghost cells only appear in local vectors, not
global, and are added on the end after the interior cells.
The type 2 'boundary' ghost cells appear in both local and global
vectors. In a local vector they are added on the end after the partition
ghost cells. In a global vector they appear straight after the interior
cells.
Is this correct? If so, I have a question:
If I'm computing fluxes between my finite volume cells, I need a local
vector to get access to both types of ghost cells.
But if I'm doing another calculation (computing fluid properties in the
cells, in this case) that does not need access to the partition ghosts,
but needs to be carried out for all interior cells *and* the boundary
ghost cells, I figure it would be preferable to do this with a global
vector (to save needless parallel communication scattering a global
vector into a local one).
However if I use DMPlexGetHeightStratum() to get the start and end
cells, the indices it returns apply to a local vector with the partition
ghosts included.
Is it safe just to subtract off the number of partition ghost cells from
the end cell index returned by DMPlexGetHeightStratum(), if I want to
loop over all interior and boundary ghosts cells in a global vector?
Cheers, Adrian
--
Dr Adrian Croucher
Department of Engineering Science
University of Auckland
New Zealand
tel 64-9-373-7599 ext 84611
