[petsc-users] KSPMonitorSingularValue

[Barry Smith]

  What happens at restart to the residual norm? That is does the residual norm change dramatically on the first iteration after the restart? This is an indication of loss of orthogonality.

   You can put in a restart of 1000 and run for 1000 iterations. What happens then?

    Barry

On Oct 26, 2011, at 9:52 AM, Klaij, Christiaan wrote:

>> You need to run for much more iterations to get any kind of reliable
>> singular values. Use something like at least -ksp_gmres_restart 100
>> -ksp_max_it 100 and see what happens to the singular values.
>> 
>>   Barry
> 
> Barry, Jed,
> 
> I followed your advice, this is what happens to the singular values
> (taking out some for readability). Do you think these values are
> reliable even though the solver doesn't converge? If so what could
> be the reason for FGMRES to stagnate?
> 
>  0 KSP Residual norm 2.069443859095e-01 % max 1 min 1 max/min 1
>  1 KSP Residual norm 2.069442759608e-01 % max 4.08809 min 4.08809 max/min 1
>  2 KSP Residual norm 2.069441760813e-01 % max 5.60619 min 4.06952 max/min 1.3776
>  3 KSP Residual norm 2.069441732278e-01 % max 9.04702 min 4.0695 max/min 2.22313
>  4 KSP Residual norm 2.069440548767e-01 % max 9.39853 min 4.06865 max/min 2.30998
>  5 KSP Residual norm 2.069439774947e-01 % max 11.5495 min 4.06865 max/min 2.83866
> 10 KSP Residual norm 2.069432503764e-01 % max 14.6194 min 4.04732 max/min 3.61213
> 20 KSP Residual norm 2.069424990159e-01 % max 22.7708 min 2.95767 max/min 7.69891
> 30 KSP Residual norm 2.069403094003e-01 % max 23.8491 min 2.93612 max/min 8.12265
> 50 KSP Residual norm 2.069374104472e-01 % max 24.0821 min 2.23473 max/min 10.7763
> 70 KSP Residual norm 2.069306551868e-01 % max 29.3557 min 2.13925 max/min 13.7224
> 100 KSP Residual norm 2.069163489527e-01 % max 29.4884 min 2.0458 max/min 14.4142
> 
> 
> dr. ir. Christiaan Klaij
> CFD Researcher
> Research & Development
> E mailto:C.Klaij at marin.nl
> T +31 317 49 33 44
> 
> MARIN
> 2, Haagsteeg, P.O. Box 28, 6700 AA Wageningen, The Netherlands
> T +31 317 49 39 11, F +31 317 49 32 45, I www.marin.nl
>