On Dec 2, 2021, at 12:55 PM, Matthew Knepley <[email protected]> wrote:

On Thu, Dec 2, 2021 at 12:07 PM Barry Smith <[email protected] <mailto:[email protected]>> wrote:

I have pushed a branch https://gitlab.com/petsc/petsc/-/merge_requests/4612 <https://gitlab.com/petsc/petsc/-/merge_requests/4612> that generates the same edge on two ranks and demonstrates the totally inappropriate PetscSF and vectors that are generated in this case (just look at the output file in the MR changes)

I will go through this carefully. However, I want to note that you are looking at the Section SF, not the Point SF.

Correct.

How many variables are there in your problem?

In this case I put one variable on each vertex and no variables on the edges (same model as for Neuron's).

Also, can you print the pointSF as well?

This can be trivially added to the example.

Thanks,

Matt

Thoughts on what we should do? I think Jed's idea of dummy vertices is very cumbersome and ugly unless it can be refined somehow. Is there a different way DMPLEX could be utilized to easily support multiple edges? Maybe not using DMPlexBuildFromCellListParallel(), but building the plex some other way? Note that it is clearly theoretically possible to have DMPlexBuildFromCellListParallel() detect a problem and error but I don't know how to do it.

Barry

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On Dec 1, 2021, at 8:00 PM, Abhyankar, Shrirang G via petsc-dev <[email protected] <mailto:[email protected]>> wrote:

From: Matthew Knepley <[email protected] <mailto:[email protected]>> Date: Wednesday, December 1, 2021 at 5:57 PM To: "Brown, Jedediah A (VISIT)" <[email protected] <mailto:[email protected]>> Cc: "Abhyankar, Shrirang G" <[email protected] <mailto:[email protected]>>, PETSc Development <[email protected] <mailto:[email protected]>>, Getnet Betrie <[email protected] <mailto:[email protected]>> Subject: Re: [petsc-dev] DMPLEX cannot support two different edges for the same two vertices, hence DMPLEX cannot?

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On Wed, Dec 1, 2021 at 6:55 PM Jed Brown <[email protected] <mailto:[email protected]>> wrote:

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Matthew Knepley <[email protected] <mailto:[email protected]>> writes:

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On Wed, Dec 1, 2021 at 5:17 PM Abhyankar, Shrirang G < [email protected] <mailto:[email protected]>> wrote:

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“You can certainly have many fields on a given edge, but I don't know what it would mean to have two edges since no topological query could tell the difference.”

The two edges in a power grid represent two parallel power lines that are connected between two locations (vertices). There are line ids (stored in the component data) to distinguish the two lines.

Yes, so you can tell the difference in the function space (since difference current passes down each one), but _topologically_ you cannot. If you put duplicate cells in, then some topological queries will give unexpected results, like the join of the two vertices.

This could be modeled with some ghost vertices. So instead of

a ------ b \_____/

you would set up

a ---o---- b \___o___/

Those ghost vertices don't have to "do" anything, but they make the edges topologically distinct.

Shri, what problems might this cause?

I don’t understand the figure you’ve drawn above. Sorry.

As a user, would I need to add anything to the way I am setting up the network/plex or any additional equations in the residual evaluation?

I do not have any issue right now for the power grid problem since I don’t require DMNetwork or DMPLEX to do the topological distinction between parallel edges. There are unique edge identifiers in my dataset through which I can make this distinction.

Yes, this would work, but it looks like the multiple cells are not causing them problems right now with the questions they are asking the mesh.

Matt

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