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<div class="moz-cite-prefix">Hi Matt,<br>
<br>
On 31/01/14 05:11, Matthew Knepley wrote:<br>
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<div class="gmail_quote">On Tue, Jan 28, 2014 at 8:57 AM,
Michael Lange <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:michael.lange@imperial.ac.uk"
target="_blank">michael.lange@imperial.ac.uk</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">Hi,<br>
<br>
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.<br>
<br>
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.<br>
<br>
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.<br>
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<div>This is true, but unfortunately not what everyone
wants. FVM people want just what is there now. This</div>
<div>same choice comes up in preallocation. There I have put
in the "center dimension" which says what</div>
<div>kind of point do you use for the center, vertex or
face? I guess we need that here as well.</div>
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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. <br>
<br>
Thanks<br>
Michael<br>
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