[petsc-users] Probelm with DMPlexExtractSubMesh

[Matthew Knepley]

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
> web: https://urldefense.us/v3/__http://docenti.unibas.it/site/home/docente.html?m=002423__;!!G_uCfscf7eWS!aNqQNIAnqfeL74GBiwHA9seVWu0ove-CSJIwX6f353WAN55As1veo1pVXphJIAAgvQIkWls9Xnm5sW-es9gN$  <https://urldefense.us/v3/__http://docenti.unibas.it/site/home/docente.html?m=002423__;!!G_uCfscf7eWS!aMKmGG4aim9XcbNSnDyHUkDyhUkQHGZ-u-xX2C-sycYUMmtTij6AwqsQbZPXJSvPp9KUfgwRJK2Ok6Me2BLgO0en1w4QF2fHo7s$>
>
>

-- 
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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