[petsc-dev] Petsc "make test" have more failures for --with-openmp=1

[Jed Brown]

Lawrence Mitchell <wence at gmx.li> writes:

>> On 19 Mar 2021, at 14:21, Jed Brown <jed at jedbrown.org> wrote:
>> 
>> Notice how the permutations are contained within the vertices {0, ..., 8}, edges {9, ..., 24}, and cells {25, ..., 32}. I would like to get rid of that restriction, but you've said it would have significant non-local consequences so I haven't tried.
>
> What we do, and I'm not sure if this is exactly what you want, is the following.
>
> Use DMPlexGetOrdering to compute permutatations of points with RCM. As you say, this is stratified.
>
> Then, we traverse cells in this RCM ordering and compute a permutation of the full plex chart greedily.
>
> Pseudo-code:
>
> permutation = empty(pstart - pend)
> i = 0
> for cell in reordered_cells:
>    points = plex.getclosure(cell)
>    for point in points:
>        if not seen(point):
>            permutation[i] = point
>            i += 1
>
> Now when we create a section, we say
>
> PetscSectionSetPermutation(sec, permutation)
>
> And then when the section offsets are calculated, the points are visited and numbered in the order provided by the permutation.
>
> This seems to work, here are the sparsity patterns for a Q3 mass matrix on an unstructured quad mesh (from gmsh). One with RCM ordering applied, the other without).

This result looks good.

> I guess the only issue is now one needs to always remember to traverse cells in the reordered_cells order (although if you call DMPlexPermute that is automatic?).

Can DMPlexPermute handle a non-stratified permutation?