[petsc-users] DMPlex and Boundary facets

[Matthew Knepley]

Okay, what Plex is saying is that Gmsh gave it a facet (a set of vertices),
but those are not the vertices
of any tetrahedral face in the mesh. It is hard to verify such a thing with
12K tets. I have definitely read in
GMsh files before with facets, so I don't think the code is completely
wrong.

Would it be possible to make a smaller mesh (10-20 cells) that shows the
same bug?

  Thanks,

     Matt

On Tue, May 18, 2021 at 12:25 PM Karin&NiKo <niko.karin at gmail.com> wrote:

> Sure! I send you both, one with the facets and one without.
>
> Thanks,
> Nicolas
>
> Le mar. 18 mai 2021 à 17:49, Matthew Knepley <knepley at gmail.com> a écrit :
>
>> On Tue, May 18, 2021 at 8:18 AM Karin&NiKo <niko.karin at gmail.com> wrote:
>>
>>> Dear PETSc team,
>>>
>>> I have tried to load a test mesh available in Gmsh' s demos directory
>>>  (share/doc/gmsh/demos/simple_geo/filter.geo, attached to this email) as a
>>> DMPlex.
>>> So I produced a msh4 file by doing :
>>>         gmsh -3 filter.geo -o /tmp/test.msh4
>>> Then I used src/dm/impls/plex/tutorials/ex2.c to load the mesh by doing :
>>>         ./ex2 -filename /tmp/test.msh4
>>>
>>> Unfortunately I get the error :
>>>
>>> [0]PETSC ERROR: --------------------- Error Message
>>> --------------------------------------------------------------
>>> [0]PETSC ERROR: No support for this operation for this object type
>>> [0]PETSC ERROR: Could not determine Plex facet for Gmsh element 1268
>>> (Plex cell 12681)
>>>
>>> The error seems to come from the fact that the msh file contains
>>> tets *and* facets *only on the Physical entities* (aka parts of the mesh
>>> boundary where
>>> the user will assign Dirichlet or Neuman conditions).
>>> If I suppress these facets by commenting  the "Physical Surface" lines
>>> in the geo file and regenerating the mesh, everything is fine.
>>>
>>> But the use of these "Physical" stuff is very common in lots of finite
>>> element codes in order to assign boundary conditions.
>>> How should I do to keep  these boundary groups of 2D elements (with
>>> corresponding names) ?
>>>
>>
>> Can you also send the *.msh file? I do not have Gmsh on this machine.
>>
>>   Thanks,
>>
>>      Matt
>>
>>
>>> Thanks for your help,
>>> Nicolas
>>>
>>>
>>>
>>
>> --
>> 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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