[petsc-users] Domain decomposition using DMPLEX

[Matthew Knepley]

On Tue, Nov 26, 2019 at 12:24 PM Danyang Su <danyang.su at gmail.com> wrote:

> On 2019-11-26 10:18 a.m., Matthew Knepley wrote:
>
> 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.
>
> Hope you are getting well soon. The mesh is not hybrid, only prism cells
> layer by layer.
>
Prism cells are called "hybrid" right now, which is indeed a bad term and I
will change.

  Thanks,

     Matt

> But the height of the prism varies significantly.
>
> Thanks,
>
> Danyang
>
>
>   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/>
>
>

-- 
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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