[petsc-users] DMPlexBuildFromCellList node ordering for tetrahedral elements

[Matthew Knepley]

On Tue, Jun 25, 2024 at 4:50 AM onur.notonur via petsc-users <
petsc-users at mcs.anl.gov> wrote:

> Hi, I'm trying to implement a Tetgen mesh importer for my
> Petsc/DMPlex-based solver. I am encountering some issues and suspect they
> might be due to my import process. The Tetgen mesh definitions can be found
> here for reference: https: //wias-berlin. de/software/tetgen/fformats.
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> Hi,
>
> I'm trying to implement a Tetgen mesh importer for my Petsc/DMPlex-based
> solver. I am encountering some issues and suspect they might be due to my
> import process. The Tetgen mesh definitions can be found here for
> reference: https://urldefense.us/v3/__https://wias-berlin.de/software/tetgen/fformats.html__;!!G_uCfscf7eWS!fZrK2yb2VL8fOhEwFSop4QgqPuB1M2_C1OMkfebpI6V32422apR69VnseJBVL8CTE5Gn4r6jRSz7K8CgmdZe$ 
> <https://urldefense.us/v3/__https://wias-berlin.de/software/tetgen/fformats.html__;!!G_uCfscf7eWS!c6srXdHHqgkq5FoeJpfHljLrP0U3UJOmz6A1-jLgkMBEtv8NTqRKgVTgoP_ArdJT5e5kx9lX53ecjbzZ3iu3-eoV4-Qq_g$>
>
> I am building DMPlex using the DMPlexBuildFromCellList function and using
> the exact ordering of nodes I get from the Tetgen mesh files (.ele file).
> The resulting mesh looks good when I export it to VTK, but I encounter
> issues when solving particular PDEs. (I can solve them while using other
> importers I write) I suspect there may be orientation errors or something
> similar.
>
> So, my question is, Is the ordering of nodes in elements important for
> tetrahedral elements while using DMPlexBuildFromCellList? If so, how should
> I arrange them?
>

Yes, TetGen inverts tetrahedra compared to Plex, since I use all outward
facing normals, whereas those in TetGen are not consistently ordered.
However, why not just use DMPlexGenerate() with TetGen?

  Thanks,

    Matt


> Thanks,
> Onur
>
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>


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