[petsc-users] Why is there MAPMPIAIJ

[Matthew Knepley]

On Thu, Feb 17, 2022 at 7:01 AM Bojan Niceno <
bojan.niceno.scientist at gmail.com> wrote:

> Dear all,
>
> I am coupling my unstructured CFD solver with PETSc.  At this moment,
> sequential version is working fine, but I obviously want to migrate to MPI
> parallel.  My code is MPI parallel since ages.
>
> Anyhow, as a part of the migration to parallel, I changed the matrix type
> from MATSEQAIJ to MATMPIAIJ.  The code compiled, but when I executed it one
> processor, I received an error message that combination of matrix format
> does not support BICG solver and PCILU preconditoner.  I took a look at the
> compatibility matrix (
> https://petsc.org/release/overview/linear_solve_table/#preconditioners)
> and noticed that MATMPIAIJ supports only MKL CParadiso preconditioner which
> seems to belong to Intel.
>
> I did some more reading and realised that I should probably continue with
> MATAIJ (which should work in sequential and parallel), but I am wondering
> why would there even be MATMPIAJ if it supports only one third-party
> preconditioner?
>

1) MATAIJ is not a concrete type, it just creates MATSEQAIJ in serial and
MATMPIAIJ in parallel

2) MATMPIAIJ supports many parallel direct solvers (see the end of
https://petsc.org/main/docs/manual/ksp/), including

  MUMPS
  SuperLU_dist
  Hypre (Euclid)
  CPardiso

There are also parallel AMG solvers, parallel DD solvers, and Krylov
solvers.

The complaint you got said that a serial LU was being used with a parallel
matrix type, so using AIJ is the right solution.

  Thanks,

     Matt


>     Cheers,
>
>     Bojan Niceno
>


-- 
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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