[petsc-users] KSP: domain decomposition and distribution

[mary sweat]

I do not explicitily check the size, because I use PETSC_DECIDE, instead I specify the number of processes. What I really care about is hw does KSPSolve solve the system in a parallel way with multiple processes.



Il Mercoledì 8 Gennaio 2014 12:34, Dave May <dave.mayhem23 at gmail.com> ha scritto:
 
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
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20140108/9a275281/attachment-0001.html>