[petsc-users] How to efficiently fill in, in parallel, a PETSc matrix from a COO sparse matrix?

[Matthew Knepley]

On Wed, Jun 21, 2023 at 12:57 PM Diego Magela Lemos <diegomagela at usp.br>
wrote:

> Unfortunately, I can modify ex2 to perform the matrix fill in using only
> one rank, although I have understood how it works.
> Is it so hard to do that?
>

It should not be. Maybe describe what is not clear? ex2 runs in parallel
now.

  Thanks,

    Matt


> Thank you.
>
>
> Em qua., 21 de jun. de 2023 às 12:20, Mark Adams <mfadams at lbl.gov>
> escreveu:
>
>> ex2 looks the same as the code at the beginning of the thread, which
>> looks fine to me, yet fails.
>> (the only thing I can think of is that &v.at(i) is not doing what one
>> wants)
>>
>> Diego: I would start with this ex2.c, add your view statement, verify;
>> incrementally change ex2 to your syntax and see where it breaks.
>>
>> Mark
>>
>> On Wed, Jun 21, 2023 at 9:50 AM Matthew Knepley <knepley at gmail.com>
>> wrote:
>>
>>> On Wed, Jun 21, 2023 at 9:22 AM Diego Magela Lemos <diegomagela at usp.br>
>>> wrote:
>>>
>>>> Please, could you provide a minimal working example (or link) of how to
>>>> do this?
>>>>
>>>
>>> You can see here
>>>
>>>   https://petsc.org/main/src/ksp/ksp/tutorials/ex2.c.html
>>>
>>> that each process only sets values for the rows it owns.
>>>
>>>   Thanks,
>>>
>>>      Matt
>>>
>>>
>>>> Thank you.
>>>>
>>>> Em ter., 20 de jun. de 2023 às 15:08, Matthew Knepley <
>>>> knepley at gmail.com> escreveu:
>>>>
>>>>> On Tue, Jun 20, 2023 at 2:02 PM Diego Magela Lemos <diegomagela at usp.br>
>>>>> wrote:
>>>>>
>>>>>> So... what do I need to do, please?
>>>>>> Why am I getting wrong results when solving the linear system if the
>>>>>> matrix is filled in with MatSetPreallocationCOO and MatSetValuesCOO?
>>>>>>
>>>>>
>>>>> It appears that you have _all_ processes submit _all_ triples (i, j,
>>>>> v). Each triple can only be submitted by a single process. You can fix this
>>>>> in many ways. For example, an easy but suboptimal way is just to have
>>>>> process 0 submit them all, and all other processes submit nothing.
>>>>>
>>>>>   Thanks,
>>>>>
>>>>>   Matt
>>>>>
>>>>>
>>>>>> Em ter., 20 de jun. de 2023 às 14:56, Jed Brown <jed at jedbrown.org>
>>>>>> escreveu:
>>>>>>
>>>>>>> Matthew Knepley <knepley at gmail.com> writes:
>>>>>>>
>>>>>>> >> The matrix entries are multiplied by 2, that is, the number of
>>>>>>> processes
>>>>>>> >> used to execute the code.
>>>>>>> >>
>>>>>>> >
>>>>>>> > No. This was mostly intended for GPUs, where there is 1 process.
>>>>>>> If you
>>>>>>> > want to use multiple MPI processes, then each process can only
>>>>>>> introduce
>>>>>>> > some disjoint subset of the values. This is also how
>>>>>>> MatSetValues() works,
>>>>>>> > but it might not be as obvious.
>>>>>>>
>>>>>>> They need not be disjoint, just sum to the expected values. This
>>>>>>> interface is very convenient for FE and FV methods. MatSetValues with
>>>>>>> ADD_VALUES has similar semantics without the intermediate storage, but it
>>>>>>> forces you to submit one element matrix at a time. Classic parallelism
>>>>>>> granularity versus memory use tradeoff with MatSetValuesCOO being a clear
>>>>>>> win on GPUs and more nuanced for CPUs.
>>>>>>>
>>>>>>
>>>>>
>>>>> --
>>>>> 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/>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20230621/6e8d8e77/attachment.html>