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
