[petsc-dev] [petsc-users] [EXTERNAL] Re: Question about periodic conditions

[Jed Brown]

Matthew Knepley <knepley at gmail.com> writes:

> We use it to identify that the mesh is periodic and in what directions, and
> use the length if we have to figure out the coordinates.
>
>> Jed may argue that he wants you to retain the far point and use L2G to
>> eliminate it, but that sounds like a lot more work.
>>
>> Computational work or implementation work?
>>
>
> implementation.

I think this is more implicit DMPlex assumptions than a fundamental issue.

>> I already have logic in DMStag to support something related, which was
>> required for L2G with INSERT_VALUES in the periodic, 1-rank case, where
>> multiple local points can respond to the same global point. So building the
>> local coordinates with the far point and then doing L2G doesn't sound bad
>> to implement, at least.
>>
>> https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/DMSTAG/DMStagPopulateLocalToGlobalInjective.html
>>
>
> That may work. It is a problem in Plex because that strategy destroys the
> topological queries. However, it sounds like you do not have that problem.

Patrick, if you're still in early stages, I would encourage you to support nodally affine maps in the L2G, which allows things like rotated periodicity for vector-valued fields.

https://gitlab.com/petsc/petsc/-/issues/566