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

[Matthew Knepley]

On Wed, Jun 9, 2010 at 12:02 AM, Andreas Hauffe <
andreas.hauffe at tu-dresden.de> wrote:

> 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?
>

Write the matrix as a PETSc binary and send it to petsc-maint at mcs.anl.gov.

   Thanks,

      Matt


> 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
>
> ----------------------------------------------------------------------------------------------------
>



-- 
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
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