[petsc-users] GMSH entities

[Matthew Knepley]

On Mon, May 13, 2024 at 10:04 PM Adrian Croucher <a.croucher at auckland.ac.nz>
wrote:

> On 14/05/24 1:44 pm, Matthew Knepley wrote:
>
> I wish GMsh was clearer about what is optional:
> https://urldefense.us/v3/__https://gmsh.info/doc/texinfo/gmsh.html*MSH-file-format__;Iw!!G_uCfscf7eWS!YJN5how37EbmfjwDvfPAsVSCQdWejJn8symxZ83hj94omk6Mh9imh2qOrFqZbsZRM_3W3G5YIn5lZK2KzQlj$ 
> They do talk about it, but not exhaustively. GMsh always writes and
> $Entities block from what I can tell.
> I can make it optional, it just might take until after the PETSc Meeting.
>
> Looks like $Entities are optional:
>
>
> https://urldefense.us/v3/__https://gitlab.onelab.info/gmsh/gmsh/-/commit/b5feba2af57181ffa946d3f0c494b014603c6efa__;!!G_uCfscf7eWS!YJN5how37EbmfjwDvfPAsVSCQdWejJn8symxZ83hj94omk6Mh9imh2qOrFqZbsZRM_3W3G5YIn5lZMbTrLlQ$ 
>
> I can also load a GMSH 4.1 file without $Entities into GMSH itself and it
> doesn't complain, suggesting that they are indeed optional.
>
> Yes, but they are not careful to specify when a file can be inconsistent.
For instance, omitting the $Entities, but then specifying entity numbers in
the $Nodes block. I think they also thought this was inconsistent, but then
got user complaints. The minimal example they show does exactly this.

> If the $Entities aren't strictly needed for anything in DMPlex (which I'm
> guessing they aren't, as the GMSH file format 2.2 doesn't even have them)
> then it would be useful not to require them.
>
I put in some code for this:
https://urldefense.us/v3/__https://gitlab.com/petsc/petsc/-/merge_requests/7546__;!!G_uCfscf7eWS!YJN5how37EbmfjwDvfPAsVSCQdWejJn8symxZ83hj94omk6Mh9imh2qOrFqZbsZRM_3W3G5YIn5lZHVFZ3e3$ 

It just ignores entity numbers when there is no section.

  Thanks,

     Matt

> - Adrian
>
> --
> Dr Adrian Croucher
> Senior Research Fellow
> Department of Engineering Science
> Waipapa Taumata Rau / University of Auckland, New Zealand
> email: a.croucher at auckland.ac.nz
> tel: +64 (0)9 923 4611
>
>

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

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