KSP Tolerances

[Matthew Knepley]

No.

On Mon, Dec 14, 2009 at 9:40 AM, Jarunan Panyasantisuk <jarunan at ascomp.ch>wrote:

> 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
>
>
>


-- 
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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