[petsc-users] Domain decomposition using DMPLEX

[Matthew Knepley]

On Tue, Nov 26, 2019 at 11:43 AM Danyang Su <danyang.su at gmail.com> wrote:

> On 2019-11-25 7:54 p.m., Matthew Knepley wrote:
>
> On Mon, Nov 25, 2019 at 6:25 PM Swarnava Ghosh <swarnava89 at gmail.com>
> wrote:
>
>> Dear PETSc users and developers,
>>
>> I am working with dmplex to distribute a 3D unstructured mesh made of
>> tetrahedrons in a cuboidal domain. I had a few queries:
>> 1) Is there any way of ensuring load balancing based on the number of
>> vertices per MPI process.
>>
>
> You can now call DMPlexRebalanceSharedPoints() to try and get better
> balance of vertices.
>
> Hi Matt,
>
> I just want to follow up if this new function can help to solve the
> "Strange Partition in PETSc 3.11" problem I mentioned before. Would you
> please let me know when shall I call this function? Right before
> DMPlexDistribute?
>
This is not the problem. I believe the problem is that you are partitioning
hybrid cells, and the way we handle
them internally changed, which I think screwed up the dual mesh for
partitioning in your example. I have been
sick, so I have not gotten to your example yet, but I will.

  Sorry about that,

    Matt

> call DMPlexCreateFromCellList
>
> call DMPlexGetPartitioner
>
> call PetscPartitionerSetFromOptions
>
> call DMPlexDistribute
>
> Thanks,
>
> Danyang
>
>
>
>> 2) As the global domain is cuboidal, is the resulting domain
>> decomposition also cuboidal on every MPI process? If not, is there a way to
>> ensure this? For example in DMDA, the default domain decomposition for a
>> cuboidal domain is cuboidal.
>>
>
> It sounds like you do not want something that is actually unstructured.
> Rather, it seems like you want to
> take a DMDA type thing and split it into tets. You can get a cuboidal
> decomposition of a hex mesh easily.
> Call DMPlexCreateBoxMesh() with one cell for every process, distribute,
> and then uniformly refine. This
> will not quite work for tets since the mesh partitioner will tend to
> violate that constraint. You could:
>
>   a) Prescribe the distribution yourself using the Shell partitioner type
>
> or
>
>   b) Write a refiner that turns hexes into tets
>
> We already have a refiner that turns tets into hexes, but we never wrote
> the other direction because it was not clear
> that it was useful.
>
>   Thanks,
>
>      Matt
>
>
>> Sincerely,
>> SG
>>
>
>
> --
> 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/>
>
>

-- 
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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