[petsc-users] Consistent domain decomposition between DMDA and DMPLEX

[Mark Adams]

On Wed, Mar 27, 2019 at 7:27 PM Matthew Knepley <knepley at gmail.com> wrote:

> On Fri, Mar 22, 2019 at 1:41 PM Swarnava Ghosh <swarnava89 at gmail.com>
> wrote:
>
>> Hi Mark and Matt,
>>
>> Thank you for your responses.
>>  "They may have elements on the unstructured mesh that intersect with any
>> number of processor domains on the structured mesh. But the unstructured
>> mesh vertices are in the structured mesh set of vertices"
>> Yes, that is correct. We would want a vertex partitioning.
>>
>
> Okay, I need to understand better what you want. A vertex partition of a
> mesh does not make sense to me. What kind
> of mesh do you have, and how do you plan to use the partitioned mesh?
>

I would guess they want a vertex partitioning to make an MatMPIAIJ. They
could inject fine (structured) grid points into coarse (unstructured)
points/vertices w/o communication. That's my best guess.


>
>   Thanks,
>
>     Matt
>
>
>> Sincerely,
>> Swarnava
>>
>> On Fri, Mar 22, 2019 at 4:08 PM Mark Adams <mfadams at lbl.gov> wrote:
>>
>>> Matt,
>>> I think they want a vertex partitioning. They may have elements on the
>>> unstructured mesh that intersect with any number of processor domains on
>>> the structured mesh. But the unstructured mesh vertices are in the
>>> structured mesh set of vertices. They want the partition of the
>>> unstructured mesh vertices (ie, matrices) to be slaved to the partitioning
>>> of the structured mesh.
>>> Do I have that right Swarnava?
>>> Mark
>>>
>>> On Fri, Mar 22, 2019 at 6:56 PM Matthew Knepley via petsc-users <
>>> petsc-users at mcs.anl.gov> wrote:
>>>
>>>> On Thu, Mar 21, 2019 at 8:20 PM Swarnava Ghosh via petsc-users <
>>>> petsc-users at mcs.anl.gov> wrote:
>>>>
>>>>> Dear PETSc users and developers,
>>>>>
>>>>> I am new to DMPLEX and had a query regarding setting up a consistent
>>>>> domain decomposition of two meshes in PETSc.
>>>>> I have a structured finite difference grid, managed through DMDA. I
>>>>> have another unstructured finite element mesh managed through DMPLEX. Now
>>>>> all the nodes in the unstructured finite element mesh also belong to the
>>>>> set of nodes in the structured finite difference mesh (but not necessarily
>>>>> vice-versa), and the number of nodes in DMPLEX mesh is less than the number
>>>>> of nodes in DMDA mesh. How can I guarantee a consistent domain
>>>>> decomposition of the two meshes? By consistent, I mean that if a process
>>>>> has a set of nodes P from DMDA, and the same process has the set of nodes Q
>>>>> from DMPLEX, then Q is a subset of P.
>>>>>
>>>>
>>>> Okay, this is not hard. DMPlexDistribute() basically distributes
>>>> according to a cell partition. You can use PetscPartitionerShell() to stick
>>>> in whatever cell partition you want. You can see me doing this here:
>>>>
>>>>
>>>> https://bitbucket.org/petsc/petsc/src/e2aefa968a094f48dc384fffc7d599a60aeeb591/src/dm/impls/plex/examples/tests/ex1.c#lines-261
>>>>
>>>> Will that work for you?
>>>>
>>>>   Thanks,
>>>>
>>>>     Matt
>>>>
>>>>
>>>>> I look forward to your response.
>>>>>
>>>>> Sincerely,
>>>>> Swarnava
>>>>>
>>>>>
>>>>
>>>> --
>>>> 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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