[petsc-users] monitoring the convergence of fieldsplit 0 and 1

[Barry Smith]

> On Apr 10, 2015, at 12:58 PM, Matthew Knepley <knepley at gmail.com> wrote:
> 
> On Fri, Apr 10, 2015 at 12:57 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> 
> > On Apr 10, 2015, at 8:07 AM, Klaij, Christiaan <C.Klaij at marin.nl> wrote:
> >
> > Barry,
> >
> > Sure, I can call PCFieldSplitGetSubKSP() to get the fieldsplit_0
> > ksp and then KSPGetIterationNumber, but what does this number
> > mean?
> >
> > It appears to be the number of iterations of the last time that
> > the subsystem was solved, right? If so, this corresponds to the
> > last iteration of the coupled system, how about all the previous
> > iterations?
> 
>    If I added a KSPGetTotalIterations() would that help?
> 
> Its hard to see how to define this consistently.

  Just count the number of iterations that KSP object has done since it was created. How could that be inconsistent?

> I think this is better handled by custom monitors.
> We could provide a default monitor for FieldSplit which does this.
> 
>   Matt
>  
> 
> Barry
> 
> >
> > Chris
> > ________________________________________
> > From: Barry Smith <bsmith at mcs.anl.gov>
> > Sent: Friday, April 10, 2015 2:48 PM
> > To: Klaij, Christiaan
> > Cc: petsc-users at mcs.anl.gov
> > Subject: Re: [petsc-users] monitoring the convergence of fieldsplit 0 and 1
> >
> >   Chris,
> >
> >     It appears you should call PCFieldSplitGetSubKSP() and then get the information you want out of the individual KSPs. If this doesn't work please let us know.
> >
> >   Barry
> >
> >> On Apr 10, 2015, at 6:48 AM, Klaij, Christiaan <C.Klaij at marin.nl> wrote:
> >>
> >> A question when using PCFieldSplit: for each linear iteration of
> >> the system, how many iterations for fielsplit 0 and 1?
> >>
> >> One way to find out is to run with -ksp_monitor,
> >> -fieldsplit_0_ksp_monitor and -fieldsplit_0_ksp_monitor. This
> >> gives the complete convergence history.
> >>
> >> Another way, suggested by Matt, is to use -ksp_monitor,
> >> -fieldsplit_0_ksp_converged_reason and
> >> -fieldsplit_1_ksp_converged_reason. This gives only the totals
> >> for fieldsplit 0 and 1 (but without saying for which one).
> >>
> >> Both ways require to somehow process the output, which is a bit
> >> inconvenient. Could KSPGetResidualHistory perhaps return (some)
> >> information on the subsystems' convergence for processing inside
> >> the code?
> >>
> >> Chris
> >>
> >>
> >> 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
> >>
> >
> 
> 
> 
> 
> -- 
> 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