Is your code sequential (with possibly OpenMP) or MPI parallel? Do you plan
to make your part of the code MPI parallel?
If it is sequential or OpenMP parallel you might consider using the new
feature https://petsc.org/release/manualpages/PC/PCMPI/#pcmpi Depending on your
system it is an easy way to run linear solver in parallel while the code is
sequential and can give some reasonable speedup.
> On Oct 26, 2023, at 8:58 AM, Qiyue Lu <[email protected]> wrote:
>
> Hello,
> I am trying to incorporate PETSc as a linear solver to compute Ax=b in my
> code. Currently, the sequential version works.
> 1) I have the global matrix A in CSR format and they are stored in three
> 1-dimensional arrays: row_ptr[ ], col_idx[ ], values[ ], and I am using
> MatCreateSeqAIJWithArrays to get the PETSc format matrix. This works.
> 2) I am trying to use multicores, and when I use "srun -n 6", I got the error
> Comm must be of size 1 from the MatCreateSeqAIJWithArrays. Saying I cannot
> use SEQ function in a parallel context.
> 3) I don't think MatCreateMPIAIJWithArrays and MatMPIAIJSetPreallocationCSR
> are good options for me, since I already have the global matrix as a whole.
>
> I wonder, from the global CSR format data, how can I reach the PETSc format
> matrix for parallel KSP computation. Are the MatSetValue, MatSetValues what I
> need?
>
> Thanks,
> Qiyue Lu
