Hi Matt,
Have you had a chance to think about the cell overlap problem? I'm
proposing to make the center dimension a general Plex attribute with the
current behaviour as the default. We can then generate the cell overlap
in DMPlexDistribute according to the center dimension using a utility
function for point adjacency, something like DMPlexGetAdjacentPoints(dm,
p).
I'm happy to provide a pull request for this change, just tell me if you
agree with this approach or if you see any problems.
Thanks and kind regards,
Michael
On 03/02/14 11:32, Michael Lange wrote:
Hi Matt,
On 31/01/14 05:11, Matthew Knepley wrote:
On Tue, Jan 28, 2014 at 8:57 AM, Michael Lange
<[email protected] <mailto:[email protected]>>
wrote:
Hi,
I noticed that the cell overlap created during DMPlexDistribute
does not include cells that only share a vertex but no edge with
an owned cell. This causes problems when performing local
assembly (MAT_IGNORE_OFF_PROC_ENTRIES) based on information from
the plex, because one contribution to the shared vertex is missing.
As an example consider the 2x2 square with 8 cells (attached).
When partitioned across two ranks with overlap=1 each rank owns 4
cells and in the current version knows about 2 halo cells, giving
a total of 6 cells. The central vertex, however, touches 3 owned
and 3 non-owned cells, one of which doesn't share an edge with
any owned cells. So, in order to correctly assemble the central
vertex locally, the rank owning it needs to know about 7 cells in
total.
I have attached a patch that fixes this problem by going over the
inverse closure of all vertices associated with a given cell
instead of using the provided edge graph. Please tell me what you
think and whether there might be an easier way to fix this.
This is true, but unfortunately not what everyone wants. FVM people
want just what is there now. This
same choice comes up in preallocation. There I have put in the
"center dimension" which says what
kind of point do you use for the center, vertex or face? I guess we
need that here as well.
Yes, I think the center dimension is exactly what we need here,
because my proposed fix is to switch from using star(cone(p)) to
star(closure(p)). So, do you want to make the center dimension a
general Plex attribute and move the Set/Get functions to plex.c? If
so, what would be the default? In that case a
DMPlexGetAdjacentPoints(dm, p) function might also be helpful if this
is used in several places? I'm happy to provide a pull request, just
tell me how you want this to be structured.
Thanks
Michael
