Solver problem

Tim Kroeger tim.kroeger at
Mon Jul 27 04:35:10 CDT 2009

Dear all,

In my application, there is a linear system to be solved in every time 
step.  Steps 0 and 1 work well, but in step 2 PETSc fails to converge. 
I suspected that the system might be unsolvable in that step and 
checked that by writing matrix and the right hand side to files and 
loading them into "octave".  Surprisingly, "octave" does find a 
solution to the system without any problems.

The problem occurs even on a single core.  I am using PETSc version 
2.3.3-p11 with the GMRES solver and ILU preconditioner.

Can anybody give me a hint which settings would PETSc reliably enable 
solving systems of the type that I face?

I have put matrix and right hand side on my homepage; they can be 
downloaded from (7MB).  In octave, I 
used the following commands to find and check the solution:

octave:1> matrix2
octave:2> vector2
octave:3> x=Mat_0\Vec_1;
octave:4> res=Mat_0*x-Vec_1;
octave:5> norm(res)
ans =  1.0032e-12
octave:6> norm(Vec_1)
ans =  27.976
octave:7> norm(Mat_0,"fro")
ans =  2.5917e+22
octave:8> norm(x)
ans =  3855.3

Best Regards,


Dr. Tim Kroeger
tim.kroeger at            Phone +49-421-218-7710
tim.kroeger at            Fax   +49-421-218-4236

Fraunhofer MEVIS, Institute for Medical Image Computing
Universitaetsallee 29, 28359 Bremen, Germany

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