[petsc-users] MatCompositeMerge + MatCreateRedundantMatrix

[Matthew Knepley]

On Tue, Mar 12, 2019 at 4:50 AM Marius Buerkle <mbuerkle at web.de> wrote:

> I tried to follow your suggestions but it seems there is
> no MPICreateSubMatricesMPI for Fortran. Is this correct?
>

We just have to write the binding. Its almost identical to
MatCreateSubMatrices() in src/mat/interface/ftn-custom/zmatrixf.c

   Matt

>
> On Wed, Feb 20, 2019 at 6:57 PM Marius Buerkle <mbuerkle at web.de> wrote:
>
>> ok, I think I understand now. I will give it a try and if there is some
>> trouble comeback to you. thanks.
>>
>
> Cool.
>
>    Matt
>
>
>>
>> marius
>>
>> On Tue, Feb 19, 2019 at 8:42 PM Marius Buerkle <mbuerkle at web.de> wrote:
>>
>>> ok, so it seems there is no straight forward way to transfer data
>>> between PETSc matrices on different subcomms. Probably doing it by "hand"
>>> extracting the matricies on the subcomms create a MPI_INTERCOMM transfering
>>> the data to PETSC_COMM_WORLD and assembling them in a new PETSc matrix
>>> would be possible, right?
>>>
>>
>> That sounds too complicated. Why not just reverse
>> MPICreateSubMatricesMPI()? Meaning make it collective on the whole big
>> communicator, so that you can swap out all the subcommunicator for the
>> aggregation call, just like we do in that function.
>> Then its really just a matter of reversing the communication call.
>>
>>    Matt
>>
>>>
>>> On Tue, Feb 19, 2019 at 7:12 PM Marius Buerkle <mbuerkle at web.de> wrote:
>>>
>>>> I see. This would work if the matrices are on different
>>>> subcommumicators ? Is it possible to add this functionality ?
>>>>
>>>
>>> Hmm, no. That is specialized to serial matrices. You need the inverse of
>>> MatCreateSubMatricesMPI().
>>>
>>>   Thanks,
>>>
>>>      Matt
>>>
>>>
>>>> marius
>>>>
>>>>
>>>> You basically need the inverse of MatCreateSubmatrices(). I do not
>>>> think we have that right now, but it could probably be done without too
>>>> much trouble by looking at that code.
>>>>
>>>>   Thanks,
>>>>
>>>>      Matt
>>>>
>>>> On Tue, Feb 19, 2019 at 6:15 AM Marius Buerkle via petsc-users <
>>>> petsc-users at mcs.anl.gov> wrote:
>>>>
>>>>> Hi !
>>>>>
>>>>> Is there some way to combine MatCompositeMerge
>>>>> with MatCreateRedundantMatrix? I basically want to create copies of a
>>>>> matrix from PETSC_COMM_WORLD to subcommunicators, do some work on each
>>>>> subcommunicator and than gather the results back to PETSC_COMM_WORLD,
>>>>> namely  I want to sum the  the invidual matrices from the subcommunicatos
>>>>> component wise and get the resulting matrix on PETSC_COMM_WORLD. Is this
>>>>> somehow possible without going through all the hassle of using MPI
>>>>> directly?
>>>>>
>>>>> marius
>>>>>
>>>>
>>>>
>>>> --
>>>> 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/>
>


-- 
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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