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

[Lawrence Mitchell]

> On 19 Mar 2021, at 03:51, Jed Brown <j...@jedbrown.org> wrote:
> 
> It's a notable weakness of DMPlex that it does not apply such an ordering of 
> dofs and I've complained to Matt about it many times over the years, but any 
> blame rests solely with me for not carving out time to implement it here.

I think there is a way to do this with plex (at least we do it), like so:

DMPlexGetOrdering(dm, MATORDERINGRCM, NULL, &isperm);

you might need to then invert this ordering.

Now when you make a section you either say

PetscSectionSetPermutation(section, isperm);

before PetscSectionSetup(section);

or, if you're using DMPlexCreateSection, pass in the isperm

This gives RCM-based ordering for the dof numbering of the section.

Cheers,

Lawrence