[petsc-users] Question on matrix assembly

[Sajid Ali]

 Hi Barry,

Thanks for creating the new function. I'm somewhat confused as to how I'd
use it. Given an MPIAIJ matrix, is one supposed to extract the local SeqAIJ
matrix and set the preallocation on each mpi-rank independently followed by
MatSetValues (on the MPIAIJ matrix) to fill the rows? Or, does one create
SeqAIJ matrices on each rank and then combine them into a parallel MPIAIJ
matrix say by using MatCreateMPIMatConcatenateSeqMat?

I tried the second approach but leaving the "number of local columns" for
MatCreateMPIMatConcatenateSeqMat as PETSC_DECIDE causes a crash (when
running with 1 mpi rank). Is this the correct approach to take and if yes
what does "number of local columns" mean when combining the seqaij matrices
?

Thank You,
Sajid Ali | PhD Candidate
Applied Physics
Northwestern University
s-sajid-ali.github.io
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