[petsc-users] KSP: domain decomposition and distribution

[Dave May]

Please check out the manual page for MatSetSizes()

http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatSetSizes.html

Basically you have two choices:

1/ Define the global size of the matrix and use PETSC_DECIDE for the local
sizes.
In this case, PETSc will define the local row size in a manner such that
there are approximately the same number of rows on each process.

2/ Define the local sizes yourself and use PETSC_DETERMINE for the global
size.
Then you have full control over the parallel layout.

The following functions described by these pages


http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatGetSize.html

http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatGetLocalSize.html

http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatGetOwnershipRanges.html

http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatGetOwnershipRangesColumn.html

might also be useful for you in double checking what the matrix
decomposition looks like


Cheers,
  Dave



On 8 January 2014 12:26, mary sweat <mary.sweat78 at yahoo.it> wrote:

> My target is the following. I got a huge linear system with a sparse huge
> matrix, nothing to deal with PDE. How is the system splitted between
> processes? is there in this suggested book the answer?
> Thanks again
>
>
>   Il Martedì 7 Gennaio 2014 17:34, Jed Brown <jedbrown at mcs.anl.gov> ha
> scritto:
>  mary sweat <mary.sweat78 at yahoo.it> writes:
>
>
> > Hi all,  I need to know how does KSP separate and distribute domain
> > between processes and the way processes share and communicate halfway
> > results. Is there any good documentation about it???
>
>
> The communication is in Mat and Vec functions.  You can see it
> summarized in -log_summary.  For the underlying theory, see Barry's
> book.
>
> http://www.mcs.anl.gov/~bsmith/ddbook.html
>
>
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