[petsc-users] dmplex normal vector incorrect for periodic gmsh grids

[Matthew Knepley]

On Tue, Dec 13, 2022 at 10:57 AM Matthew Knepley <knepley at gmail.com> wrote:

> On Tue, Dec 13, 2022 at 6:11 AM Praveen C <praveen at gmx.net> wrote:
>
>> Hello
>>
>> In the attached test, I read a small grid made in gmsh with periodic bc.
>>
>> This is a 2d mesh.
>>
>> The cell numbers are shown in the figure.
>>
>> All faces have length = 2.5
>>
>> But using PetscFVFaceGeom I am getting length of 7.5 for some faces.
>> E.g.,
>>
>> face: 59, centroid = 3.750000, 2.500000, normal = 0.000000, -7.500000
>>
>> ===> Face length incorrect = 7.500000, should be 2.5
>>
>> support[0] = 11, cent = 8.750000, 3.750000, area = 6.250000
>>
>> support[1] = 15, cent = 8.750000, 1.250000, area = 6.250000
>>
>>
>> There are also errors in the orientation of normal.
>>
>> If we disable periodicity in geo file, this error goes away.
>>
>
> Yes, by default we only localize coordinates for cells. I can put in code
> to localize faces.
>

Okay, I now have a MR for this:
https://gitlab.com/petsc/petsc/-/merge_requests/5917

I am attaching your code, slightly modified. You can run

  ./dmplex -malloc_debug 0 -dm_plex_box_upper 10,10 -dm_plex_box_faces 4,4
-dm_plex_simplex 0 -dm_view ::ascii_info_detail -draw_pause 3
-dm_plex_box_bd periodic,periodic -dm_localize_height 0

which shows incorrect edges and

./dmplex -malloc_debug 0 -dm_plex_box_upper 10,10 -dm_plex_box_faces 4,4
-dm_plex_simplex 0 -dm_view ::ascii_info_detail -draw_pause 3
-dm_plex_box_bd periodic,periodic -dm_localize_height 1

which is correct. If you want to control things yourself, instead of using
the option you can call DMPlexSetMaxProjectionHeight() on the coordinate DM
yourself.

  Thanks,

     Matt


>   Thanks,
>
>     Matt
>
>
>> Thanks
>> praveen
>>
> --
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> experiments lead.
> -- Norbert Wiener
>
> https://www.cse.buffalo.edu/~knepley/
> <http://www.cse.buffalo.edu/~knepley/>
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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