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

[Praveen C]

Thank you, this MR works if I generate the mesh within the code.

But using a mesh made in gmsh, I see the same issue.

Thanks
praveen

> On 14-Dec-2022, at 12:51 AM, Matthew Knepley <knepley at gmail.com> wrote:
> 
> On Tue, Dec 13, 2022 at 10:57 AM Matthew Knepley <knepley at gmail.com <mailto:knepley at gmail.com>> wrote:
>> On Tue, Dec 13, 2022 at 6:11 AM Praveen C <praveen at gmx.net <mailto: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
>> -- 
>> 

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