dolfin team mailing list archive

["H. Etzel" <hetzel.devel@xxxxxx>]

Like the message is telling.
The matrix is bad conditioned, but it values are not zero if the tolerance
is not 1e-12 but 1e-20.
So the question is how to change the tolerance.

/Haiko

-----Ursprüngliche Nachricht-----
Von: dolfin-dev-bounces@xxxxxxxxxx [mailto:dolfin-dev-bounces@xxxxxxxxxx] Im
Auftrag von Anders Logg
Gesendet: Donnerstag, 22. Dezember 2005 16:20
An: Discussion of DOLFIN development
Betreff: Re: [DOLFIN-dev] zero pivot


Looks like you are trying to solve a singular system. Most likely,
something is wrong with the matrix which PETSc rightly detects.

To be sure, try exporting the matrix to MATLAB/Octave and see if you
can invert it there or compute the condition number:

File file("matrix.m");
file << A;

Then just type

    matrix

in MATLAB/Octave and check if it looks ok.

/Anders


On Thu, Dec 22, 2005 at 04:02:19PM +0100, hetzel.devel@xxxxxx wrote:
> Hello everyone,
> I get a problem with my solver.
> I'm using the LU or alternative the GMRES solver, but by solving my
System, I always get the following message from Petsc:
> 
> [0]PETSC ERROR: MatLUFactorNumeric_SeqAIJ() line 516 in
src/mat/impls/aij/seq/aijfact.c
> [0]PETSC ERROR: Detected zero pivot in LU factorization
> see
http://www.mcs.anl.gov/petsc/petsc-as/documentation/troubleshooting.html#Zer
oPivot!
> [0]PETSC ERROR: Zero pivot row 2950 value 4.17812e-13 tolerance 1e-12 * rs
0.450719!
> [0]PETSC ERROR: MatLUFactorNumeric() line 1994 in
src/mat/interface/matrix.c
> [0]PETSC ERROR: PCSetUp_ILU() line 798 in
src/ksp/pc/impls/factor/ilu/ilu.c
> [0]PETSC ERROR: PCSetUp() line 798 in src/ksp/pc/interface/precon.c
> [0]PETSC ERROR: KSPSetUp() line 234 in src/ksp/ksp/interface/itfunc.c
> [0]PETSC ERROR: KSPSolve() line 332 in src/ksp/ksp/interface/itfunc.c
> 
> Is there an option for the solver to set the tolerance?
> 
> /Haiko
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-- 
Anders Logg
Research Assistant Professor
Toyota Technological Institute at Chicago
http://www.tti-c.org/logg/

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