[petsc-users] [petsc-dev] Two questions about PC Object

[Hong Zhang]

Gabriele:

> However, I am running into problems with the matrices that correspond to a
> different problem type. I get results when using MUMPS, but they differ
> widely from the Scalapack results. With MUMPS I get an error like:
> Error reported by MUMPS in numerical factorization phase: INFO(1)=-1,
> INFO(2)=359

Checking mumps manual, "INFO(1)=-1,
INFO(2)=359" means an error occurred on processor 359. How many
processors do you use,
more than 359?

> I noticed that for the matrix types where I get good results, the nonzeros
> reported for the PC Object type exactly the number of entries in my input
> data for the matrix (MPIAIJ format). For the type that does not work, petsc
> reports more nonzeros than what I enter. The message looks like this:
>   linear system matrix = precond matrix:
>   Matrix Object:
>     type=mpiaij, rows=123120, cols=123120
>     total: nonzeros=59094408, allocated nonzeros=59173613
> My questions are:
> 1) Does anybody know what the error INFO(1)=-1 means in MUMPS?

Check mumps manual ~petsc/externalpackages/MUMPS_xxx/doc/userguide_xxx.pdf

> 2) How does PETSc calculate the number of nonzeros for the PC matrix?

When using mumps, mumps computes the nonzeros of  the PC matrix.
Factored matrix is far more denser than original matrix in general.
Mumps sets default fill-in ratio as 20,
which may still insufficient sometimes. You may experiment with
different matrix orderings
-mat_mumps_icntl_7 <mat_ordering>. Are you using petsc-dev with the
latest mumps 4.10?
If so, you may turn on parallel symbolic factorization '-mat_mumps_icntl_28 2'.

Good luck,

Hong
> Have banging my head against this problem for a while. Any advice is highly
> appreciated.
> Many thanks in advance!
> Gabriele Jost
> Texas Advanced Computing Center
>
>