[petsc-users] DMPlexBuildFromCellList node ordering for tetrahedral elements

[onur.notonur]

In my workflow, I was trying to use multiple mesh sources, and to achieve that, I converted them to an HDF5 file along with all other complementary information regarding my PDE. This approach seemed beneficial at first, but it's hard to manage now. (Also, I didn't know about DMPlexGenerate() :) ) However, thanks to you, I see I need to inspect the tetgenerate.cxx file. Thank you very much!

Thanks,
Onur

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On Tuesday, June 25th, 2024 at 2:11 PM, Matthew Knepley <knepley at gmail.com> wrote:

> 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. htmlI
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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*(https:/*urldefense.us/v3/__https:/*wias-berlin.de/software/tetgen/fformats.html__;!!G_uCfscf7eWS!c6srXdHHqgkq5FoeJpfHljLrP0U3UJOmz6A1-jLgkMBEtv8NTqRKgVTgoP_ArdJT5e5kx9lX53ecjbzZ3iu3-eoV4-Qq_g$)__;XS8v!!G_uCfscf7eWS!YhhAyOWDVeQm_MzXouB0hyFqonqeV1Ds-awndO2XWRhhfqTAwYpejwkiZTw0ayB3NhhOZiJ1f6k-BSQdaNhcYww5f6pyCw$ 
>>
>> 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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