[petsc-users] Domain decomposition using DMPLEX

[Danyang Su]

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 
> <mailto: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?

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/>
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