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

[Diego Magela Lemos]

Please, could you provide a minimal working example (or link) of how to do
this?
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/>
>
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