[petsc-users] How to combine different element types into a single DMPlex?

[Matthew Knepley]

On Tue, Sep 21, 2021 at 10:31 AM Karin&NiKo <niko.karin at gmail.com> wrote:

> Dear Eric, dear Matthew,
>
> I share Eric's desire to be able to manipulate meshes composed of
> different types of elements in a PETSc's DMPlex.
> Since this discussion, is there anything new on this feature for the
> DMPlex object or am I missing something?
>

Thanks for finding this!

Okay, I did a rewrite of the Plex internals this summer. It should now be
possible to interpolate a mesh with any
number of cell types, partition it, redistribute it, and many other
manipulations.

You can read in some formats that support hybrid meshes. If you let me know
how you plan to read it in, we can make it work.
Right now, I don't want to make input interfaces that no one will ever use.
We have a project, joint with Firedrake, to finalize
parallel I/O. This will make parallel reading and writing for checkpointing
possible, supporting topology, geometry, fields and
layouts, for many meshes in one HDF5 file. I think we will finish in
November.

  Thanks,

     Matt


> Thanks,
> Nicolas
>
> Le mer. 21 juil. 2021 à 04:25, Eric Chamberland <
> Eric.Chamberland at giref.ulaval.ca> a écrit :
>
>> Hi,
>> On 2021-07-14 3:14 p.m., Matthew Knepley wrote:
>>
>> On Wed, Jul 14, 2021 at 1:25 PM Eric Chamberland <
>> Eric.Chamberland at giref.ulaval.ca> wrote:
>>
>>> Hi,
>>>
>>> while playing with DMPlexBuildFromCellListParallel, I noticed we have to
>>> specify "numCorners" which is a fixed value, then gives a fixed number
>>> of nodes for a series of elements.
>>>
>>> How can I then add, for example, triangles and quadrangles into a DMPlex?
>>>
>>
>> You can't with that function. It would be much mich more complicated if
>> you could, and I am not sure
>> it is worth it for that function. The reason is that you would need index
>> information to offset into the
>> connectivity list, and that would need to be replicated to some extent so
>> that all processes know what
>> the others are doing. Possible, but complicated.
>>
>> Maybe I can help suggest something for what you are trying to do?
>>
>> Yes: we are trying to partition our parallel mesh with PETSc functions.
>> The mesh has been read in parallel so each process owns a part of it, but
>> we have to manage mixed elements types.
>>
>> When we directly use ParMETIS_V3_PartMeshKway, we give two arrays to
>> describe the elements which allows mixed elements.
>>
>> So, how would I read my mixed mesh in parallel and give it to PETSc
>> DMPlex so I can use a PetscPartitioner with DMPlexDistribute ?
>>
>> A second goal we have is to use PETSc to compute the overlap, which is
>> something I can't find in PARMetis (and any other partitionning library?)
>>
>> Thanks,
>>
>> Eric
>>
>>
>>
>>   Thanks,
>>
>>       Matt
>>
>>
>>
>>> Thanks,
>>>
>>> Eric
>>>
>>> --
>>> Eric Chamberland, ing., M. Ing
>>> Professionnel de recherche
>>> GIREF/Université Laval
>>> (418) 656-2131 poste 41 22 42
>>>
>>>
>>
>> --
>> 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
>>
>> https://www.cse.buffalo.edu/~knepley/
>> <http://www.cse.buffalo.edu/~knepley/>
>>
>> --
>> Eric Chamberland, ing., M. Ing
>> Professionnel de recherche
>> GIREF/Université Laval
>> (418) 656-2131 poste 41 22 42
>>
>>

-- 
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

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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