KSP Tolerances

[Jarunan Panyasantisuk]

Thank you. I see it.
I also see in the output file that sometimes the initial residual
||r_0|| = ||b|| is simply rnorm ||r||  at iteration 0. Does it change
the reference during the computation?

Jarunan


Matthew Knepley wrote:
> You can see in the info output what is happening. The test is
>
>   rnorm >= ksp->divtol*ksp->rnorm0
>
> Here ||r_0|| = ||b|| = 0.00331536 and ||r|| = 513.979, and thus it results
> in divergence. It appears that ILU(0) is very bad for this problem.
>
>    Matt
>
> On Mon, Dec 14, 2009 at 9:07 AM, <jarunan at ascomp.ch
> <mailto:jarunan at ascomp.ch>> wrote:
>
>     Hi,
>
>     Thank you for your advice. With this mail I attach the output file
>     run.log.
>     My grid is 2-level grid. The coarse grid is computed first then
>     the fine grid. The problem occur in the fine grid. You can see at
>     lines 3098, 4552 and 6127 where it is diverged.
>
>     Regards,
>     Jarunan
>
>
>
>     Quoting Matthew Knepley <knepley at gmail.com
>     <mailto:knepley at gmail.com>>:
>
>         Run with -ksp_view -ksp_monitor -info and send us all the output.
>
>          Matt
>
>         On Mon, Dec 14, 2009 at 8:36 AM, <jarunan at ascomp.ch
>         <mailto:jarunan at ascomp.ch>> wrote:
>
>
>             Dear Petsc Team,
>
>             There is something not clear for me about divergence
>             tolerance. Firstly, my
>             computation diverges with the reason of dtol (-4), which
>             was set by default
>             (10000). When I increased dtol to 1.0e+8, it became
>             converged. However, the
>             relative residual where it was diverged is less than the
>             default dtol. I
>             would like to know, how it is exactly calculated.
>
>             ----------I describe my problem more in detail
>             here.-------------------
>             As I set the tolerances for the solver as below, my
>             problem diverges with
>             converged reason -4 (from divergence tolerance)
>
>             call KSPSetTolerances(ksp,1.0e-06,1.0e-20,
>             PETSC_DEFAULT_DOUBLE_PRECISION,10000,ierr)
>
>             I monitor the residual. it printed the information below
>             and quit the
>             computation.(I delete the true residual norm and Ax/Ae.
>             Please tell me if
>             you need them.)
>
>              0 KSP preconditioned resid norm 5.139790011051e+02
>
>             With -ksp_view, it shows that default value of dtol is
>             10000. I increased
>             dtol to 1.0e+8, then the solver solved the problem. With
>             -ksp_monitor_true_residual, the first 5 iterations read:
>
>              0 KSP preconditioned resid norm 5.139790011051e+02
>              1 KSP preconditioned resid norm 1.840751662590e+01
>              2 KSP preconditioned resid norm 3.653339750400e+00
>              3 KSP preconditioned resid norm 2.538794826933e+00
>              4 KSP preconditioned resid norm 2.299844715275e-01
>
>             Here, from iteration 0 to iteration 1,the relative
>             residual is 0.03580,
>             much less than 1.0e+4 the default dtol value. So, why was
>             it diverged at the
>             first time?
>
>             ----------------------------------------------------------------------------
>
>             Regards,
>             Jarunan
>
>
>
>
>             --
>             Jarunan Panyasantisuk
>             Development Engineer
>             ASCOMP GmbH, Technoparkstr. 1
>             CH-8005 Zurich, Switzerland
>             Phone : +41 44 445 4072
>             Fax   : +41 44 445 4075
>             E-mail: jarunan at ascomp.ch <mailto:jarunan at ascomp.ch>
>             www.ascomp.ch <http://www.ascomp.ch>
>
>
>
>
>         --
>         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
>
>
>
>
>     -- 
>     Jarunan Panyasantisuk
>     Development Engineer
>     ASCOMP GmbH, Technoparkstr. 1
>     CH-8005 Zurich, Switzerland
>     Phone : +41 44 445 4072
>     Fax   : +41 44 445 4075
>     E-mail: jarunan at ascomp.ch <mailto:jarunan at ascomp.ch>
>     www.ascomp.ch <http://www.ascomp.ch>
>
>
>
>
> -- 
> 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


-- 
Jarunan Panyasantisuk
Development Engineer
ASCOMP GmbH, Technoparkstr. 1
CH-8005 Zurich, Switzerland
Phone : +41 44 445 4072
Fax   : +41 44 445 4075
E-mail: jarunan at ascomp.ch
www.ascomp.ch