[petsc-users] markers

[Matthew Knepley]

On Sun, Feb 2, 2025 at 3:59 PM Aldo Bonfiglioli <aldo.bonfiglioli at unibas.it>
wrote:

> Dear all,
>
> it is unclear to me what is being flagged with the "marker" flag when a
> mesh is created using DMPlexCreate.
>
> The 2D triangular mesh pictured in the enclosed pdf has the following
> features:
>
> DM Object: 2D plex 1 MPI process
>  type: plex
> 2D plex in 2 dimensions:
>  Number of 0-cells per rank: 12
>  Number of 1-cells per rank: 23
>  Number of 2-cells per rank: 12
> Labels:
>  celltype: 3 strata with value/size (0 (12), 1 (23), 3 (12))
>  depth: 3 strata with value/size (0 (12), 1 (23), 2 (12))
>  marker: 1 strata with value/size (1 (20))
>  Face Sets: 4 strata with value/size (1 (3), 2 (2), 3 (3), 4 (2))
>
> i.e 12 gridpoints, 23 edges and 12 triangular cells.
>
> When I call DMGetStratumSize at stratum 0 to 2, this is what I get.
>
> CreateSectionAlternate DMGetStratumSize found            0  'marker'
> points @ depth            0  on PE#            0
> CreateSectionAlternate DMGetStratumSize found           20  'marker'
> points @ depth            1  on PE#            0
> CreateSectionAlternate DMGetStratumSize found            0  'marker'
> points @ depth            2  on PE#            0
>
> Is the marker flagging boundary edges or boundary vertices (nodes) ? In
> any case, why are there 20, instead of 10?
>

By default the "marker" label marks all k-cells on the boundary. In this
case it means

  10 vertices + 10 edges = 20 points

You can see what is in the label using

  -dm_view -dm_plex_view_labels marker

with

  DMViewFromOptions(dm, NULL, "-dm_view")

in your code.

Finally: I believe face sets refers to boundary faces, where each side of
> the square domain has been given a different flag.
>
> Yes.

> How do I access the face sets information ?
>
DMLabel label;

PetscCall(DMGetLabel(dm, "Face Sets", &label));

  Thanks,

     Matt

> Thanks,
>
> Aldo
>
>
> --
> Dr. Aldo Bonfiglioli
> Associate professor of Fluid Machines
> Scuola 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!Zs0PBHmkwRS6C-HyPNWsfCXfxTmHZ51FTqXs6A-ujrSlUUYpguXpO2Cg1tShryNL4k0RYpZVhUjgM7T7j789$  <https://urldefense.us/v3/__http://docenti.unibas.it/site/home/docente.html?m=002423__;!!G_uCfscf7eWS!c6_YYKL6k6FdMvXiZuhIJ2t5rbgB45aqicDR0WpLsZSgrs7NO0SMggi_L8KB2ZKd-w8JlcGQJTFm-uotq1RhZRDxD575sfToW2A$>
>
>

-- 
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experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

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