[petsc-users] positive definite MPISBAIJ-Matrix gets singular in the case of more than one MPI-process

[Andreas Hauffe]

I tried to find out if the matrix gets corrupted in the multiple process case. 
So I wrote both matrices (single/multiple process) to an ASCII file. Both 
files contained the same matrix. The diff command printed no difference.

I use a MPISBAIJ matrix. So I think it is impossible to create an unsymmetric 
matrix. Is this right?

Andreas

Am Dienstag 08 Juni 2010 17:59:01 schrieb Matthew Knepley:
> On Tue, Jun 8, 2010 at 12:33 AM, Andreas Hauffe <
>
> andreas.hauffe at tu-dresden.de> wrote:
> > Dear all,
> >
> > I want to solve a linear System with a symmetric positive definite
> > matrix. I
> > use the external package MUMPS as solver with the following commands
> >
> >  call KSPCreate(PETSC_COMM_WORLD,ksp,ierr)
> >  call KSPSetOperators(ksp,mat,mat,DIFFERENT_NONZERO_PATTERN,ierr)
> >  call KSPSetType(ksp,KSPPREONLY,ierr)
> >  call KSPGetPC(ksp,prec,ierr)
> >  call PCSetType(prec,PCCHOLESKY,ierr)
> >  call PCFactorSetMatSolverPackage(prec,MAT_SOLVER_MUMPS,ierr)
> >  call KSPSetFromOptions(ksp,ierr)
> >  call KSPSolve(ksp,vec1,vec2,ierr)
> >
> > and give the option "-mat_mumps_sym 1" (symmetric positive definite).
> >
> > If I run the program with one MPI-process everything works fine. For a
> > low number of unknows it also works for more MPI-processes. If I increase
> > the number of unknows (>50000) and use more then one MPI-process on one
> > or more host, I get a MUMPS error that the matrix is singular. With one
> > MPI-process everything is still fine. The critical value for the number
> > of unknows depends also on the use of the debug-version or
> > non-debug-version of PETSc. If I do not use the option "-mat_mumps_sym 1"
> > everything also works.
>
> It sounds like your matrix is not actually symmetric on multiple processes:
>
> http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpa
>ges/Mat/MatIsSymmetric.html
>
>     Matt
>
> > Right now the finite element assembling process (MatSetValue) is only
> > done with rank 0. So the hole matrix gets all its values only from rank
> > 0.
> >
> > Could someone explain this behaviour? Where is my error?
> >
> > Btw, I am currently using PETSc 3.0 since I work with SLEPc as well.
> >
> > Thank you very much,
> > --
> > Andreas Hauffe
> >
> >
> > -------------------------------------------------------------------------
> >--------------------------- Technische Universität Dresden
> > Institut für Luft- und Raumfahrttechnik / Institute of Aerospace
> > Engineering
> > Lehrstuhl für Luftfahrzeugtechnik / Chair of Aircraft Engineering
> >
> > D-01062 Dresden
> > Germany
> >
> > phone   : (++49)351 463 38496
> > fax     : (++49)351 463 37263
> > mail    : andreas.hauffe at tu-dresden.de
> > Website : http://tu-dresden.de/mw/ilr/lft
> >
> > -------------------------------------------------------------------------
> >---------------------------



-- 
Andreas Hauffe

----------------------------------------------------------------------------------------------------
Technische Universität Dresden
Institut für Luft- und Raumfahrttechnik / Institute of Aerospace Engineering
Lehrstuhl für Luftfahrzeugtechnik / Chair of Aircraft Engineering

D-01062 Dresden
Germany

phone   : (++49)351 463 38496
fax     : (++49)351 463 37263
mail    : andreas.hauffe at tu-dresden.de
Website : http://tu-dresden.de/mw/ilr/lft
----------------------------------------------------------------------------------------------------