[petsc-users] Probelm with DMPlexExtractSubMesh

[Aldo Bonfiglioli]

On 11/13/25 19:48, Matthew Knepley wrote:
> Sorry, I have been traveling. I just got back to this.
>
> The problem is that _everything_ that goes in the submesh has to have 
> the same label value. That way you can distinguish exactly what you 
> want in. However, the boundary label has to make decisions about 
> shared edges and vertices. I am attaching a modified code that does 
> what you want by making a separate label for each side.
>
> I apologize for the C. I am just not as quick in Fortran.
>
>   Thanks,
>
>      Matt
>
> On Thu, Nov 6, 2025 at 1:42 AM Aldo Bonfiglioli 
> <aldo.bonfiglioli at unibas.it> wrote:
>
>     Dear all,
>
>     I am having troubles in using DMPlexExtractSubMesh to extract the
>     different strata of the Face Sets of a given mesh.
>
>     When run on the enclosed tetrahedral mesh of the unit cube
>     generated with gmsh
>
>>     Face Sets: 6 strata with value/size (1 (246), 2 (246), 3 (246), 4
>>     (246), 5 (242), 6 (242))
>>
>     I would expect 246 "points" on stratum 3, but when I DMview the
>     subdm (and plot it) the surface mesh looks incomplete
>
>>     DM Object: patch_03 1 MPI process
>>      type: plex
>>     patch_03 in 2 dimensions:
>>      Cells are at height 1
>>      Number of 0-cells per rank: 122
>>      Number of 1-cells per rank: 325
>>     Number of 2-cells per rank: 204
>>     Number of 3-cells per rank: 204 [204]
>>     Labels:
>>     celltype: 4 strata with value/size (0 (122), 1 (325), 3 (204), 12
>>     (204))
>>     depth: 4 strata with value/size (0 (122), 1 (325), 2 (204), 3 (204))
>>     Cell Sets: 1 strata with value/size (1 (204))
>>     Face Sets: 1 strata with value/size (3 (204))
>>     Edge Sets: 2 strata with value/size (1 (8), 5 (8))
>>
>     see also patch_03.pdf
>
>     What am I doing wrong?
>
>     A simple reproducer (compiles with petsc-3.24.0) and the gmsh mesh
>     are enclosed.
>
>     Thanks,
>
>     Aldo
>
>     -- 
>     Dr. Aldo Bonfiglioli
>     Associate professor of Fluid Mechanics
>     Dipartimento di Ingegneria
>     Universita' della Basilicata
>     V.le dell'Ateneo Lucano, 10 85100 Potenza ITALY
>     tel:+39.0971.205203 fax:+39.0971.205215
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>
>
>
> -- 
> 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
>
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Matthew,

thank you for providing the working C code.

I will ba back to you in case I need further advice.

Regards,

Aldo

-- 
Dr. Aldo Bonfiglioli
Associate professor of Fluid Mechanics
Dipartimento di Ingegneria
Universita' della Basilicata
V.le dell'Ateneo Lucano, 10 85100 Potenza ITALY
tel:+39.0971.205203 fax:+39.0971.205215
web:https://urldefense.us/v3/__http://docenti.unibas.it/site/home/docente.html?m=002423__;!!G_uCfscf7eWS!abF6mWj2v5ivSvUET6QFY34S5Jw6daKMHiS5E9ztz2YbV2jQPr-0WGi09d7IEArZlAwqdLwjjsQeUl2PlNwJMcq6AAnRpMwHc3Q$ 
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