[petsc-users] parallelize matrix assembly process

[Junchao Zhang]

Since you run with multiple ranks, you should use matrix type mpiaij and
MatMPIAIJSetPreallocation. If preallocation is difficult to estimate, you
can use MatPreallocator, see an example at
https://gitlab.com/petsc/petsc/-/blob/main/src/mat/tests/ex230.c

--Junchao Zhang


On Mon, Dec 12, 2022 at 5:16 AM 김성익 <ksi2443 at gmail.com> wrote:

> Hello,
>
>
> I need some keyword or some examples for parallelizing matrix assemble
> process.
>
> My current state is as below.
> - Finite element analysis code for Structural mechanics.
> - problem size : 3D solid hexa element (number of elements : 125,000),
> number of degree of freedom : 397,953
> - Matrix type : seqaij, matrix set preallocation by using
> MatSeqAIJSetPreallocation
> - Matrix assemble time by using 1 core : 120 sec
>    for (int i=0; i<125000; i++) {
>     ~~ element matrix calculation}
>    matassemblybegin
>    matassemblyend
> - Matrix assemble time by using 8 core : 70,234sec
>   int start, end;
>   VecGetOwnershipRange( element_vec, &start, &end);
>   for (int i=start; i<end; i++){
>    ~~ element matrix calculation
>    matassemblybegin
>    matassemblyend
>
>
> As you see the state, the parallel case spent a lot of time than
> sequential case..
> How can I speed up in this case?
> Can I get some keyword or examples for parallelizing assembly of matrix in
> finite element analysis ?
>
> Thanks,
> Hyung Kim
>
>
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