MeshWorker and assembly on periodic faces

[Praveen C]

Dear all

Suppose I have a 2d square domain with periodicity in both directions.

I loop over faces with MeshWorker::mesh_loop, specify assemble_flags as below

    auto assemble_flags = MeshWorker::assemble_own_cells;
      assemble_flags |= MeshWorker::assemble_own_interior_faces_once;
      assemble_flags |= MeshWorker::assemble_ghost_faces_once;

Suppose face1 and face2 are periodic pairs of faces. Will the above mesh_loop ensure that only one of face1 or face2 is visited during assembly ?

Or will it visit both periodic face pairs ?

thanks

praveen

[Wolfgang Bangerth]

On 3/3/26 03:09, Praveen C wrote:
>
> I loop over faces with MeshWorker::mesh_loop, specify assemble_flags as below
>
>     auto assemble_flags = MeshWorker::assemble_own_cells;
>       assemble_flags |= MeshWorker::assemble_own_interior_faces_once;
>       assemble_flags |= MeshWorker::assemble_ghost_faces_once;
>
> Suppose face1 and face2 are periodic pairs of faces. Will the above mesh_loop
> ensure that only one of face1 or face2 is visited during assembly ?
>
> Or will it visit both periodic face pairs ?

Praveen:
I'm not sure whether anyone knows for certain what the answer to your question
is. But why not write a small program to find out and, if possible, update the
documentation with your findings?

Best
W.

[Luca Heltai]

Dear Praveen,

to add to what Wolfgang said: I implemented the first version of MeshWorker::mesh_loop function, and at the time periodicity was not supported. Unless someone else implemented the logic for periodic faces later on, I would assume that they are treated as boundary faces.

We’d of course be very happy to review a patch that adds the correct behaviour for periodic faces!

:)

L

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[Praveen C]

Thank you both for the suggestions.

Periodic faces should be treated as interior faces and then the flag MeshWorker::assemble_own_interior_faces_once should apply and only one of the periodic face pairs should be used for assembly, even though physically they are different faces.

I want to make sure this is happening, and will write some small test code.

The code of mesh_loop is checking about periodicity, but the logic is not clear to me from reading the code.

I have used these features in a DG code (and I am sure many others also) and it seems to work as expected. But I do observe some issues on gmsh grids when I use periodicity, but maybe it is not related to MeshWorker. I will post a separate issue on this.

best
praveen

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[Praveen C]

I made a small example to test this

https://codeberg.org/cpraveen/deal_ii/src/branch/master/periodic_faces

and explain the output in the readme.

The conclusion is that periodic faces are treated as interior faces. So if the flag

MeshWorker::assemble_own_interior_faces_once

is given, then among a periodic face pair, only one of them is visited by mesh_loop, which is what we want.

In the documentation on AssembleFlags

https://dealii.org/current/doxygen/deal.II/namespaceMeshWorker.html#ac7a9db8b34d398d7d398d1e8809874aa

the behaviour of periodic faces can be mentioned, that they are treated as interior faces for assembly.

thanks

praveen

To view this discussion visit https://groups.google.com/d/msgid/dealii/FC044ECE-4FB2-4FB3-A3B4-F07FBFA7350E%40gmail.com.

[Wolfgang Bangerth]

Hi Praveen:

> I made a small example to test this
>
> https://codeberg.org/cpraveen/deal_ii/src/branch/master/periodic_faces

Nice! I made this example into a test case here:
https://github.com/dealii/dealii/pull/19372

> The conclusion is that periodic faces are treated as interior faces. So if the
> flag
>
>>>> MeshWorker::assemble_own_interior_faces_once
>
> is given, then among a periodic face pair, only one of them is visited by
> mesh_loop, which is what we want.
>
> In the documentation on AssembleFlags
>
> https://dealii.org/current/doxygen/deal.II/

> namespaceMeshWorker.html#ac7a9db8b34d398d7d398d1e8809874aa <https://
> nam10.safelinks.protection.outlook.com/?
> url=https%3A%2F%2Fdealii.org%2Fcurrent%2Fdoxygen%2Fdeal.II%2FnamespaceMeshWorker.html%23ac7a9db8b34d398d7d398d1e8809874aa&data=05%7C02%7CWolfgang.Bangerth%40colostate.edu%7C820690ed1007446714f008de79cc687c%7Cafb58802ff7a4bb1ab21367ff2ecfc8b%7C0%7C0%7C639082116041932601%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=X1Oe8HE9aK7Ro7zP76oiOr5sEEgbYM877Q51b3tsNaw%3D&reserved=0>

>
> the behaviour of periodic faces can be mentioned, that they are treated as
> interior faces for assembly.

Would you like to write a patch that describes this? The flags are declared
and documented in
include/deal.II/meshworker/assemble_flags.h
It would be great to update the documentation to match what you found!

Best
Wolfgang