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

[Matthew Knepley]

On Thu, Mar 28, 2019 at 7:24 PM Swarnava Ghosh <swarnava89 at gmail.com> wrote:

> Hi Mark and Matt,
>
> I calculate my unknown fields at the nodes of my coarse unstructured mesh,
> and then project the solution at some of the fine structured mesh nodes.
> The only global matrix I form is on the unstructured coarse mesh to do a
> Poisson solve.
>

Is this a finite element Poisson solve on your coarse unstructured mesh?

  Thanks,

    Matt


> Sincerely,
> Swarnava
>
> On Thu, Mar 28, 2019 at 5:56 AM Mark Adams <mfadams at lbl.gov> wrote:
>
>>
>>>
>>> That seems like a bad tradeoff. You avoid one communication during
>>> injection for at least that much or more during
>>> FE assembly on that cell partition?
>>>
>>>
>> I am just guessing about the purpose as a way to describing what they are
>> asking for.
>>
>>
>>>   Matt
>>>
>>>
>>>>
>>>>>   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/>
>>>>>
>>>>
>>>
>>> --
>>> 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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