[petsc-dev] bad advice? TSStep has failed due to DIVERGED_NONLINEAR_SOLVE, increase -ts_max_snes_failures or make negative to attempt recovery!

[Nathan Collier]

I know that all I actually see when I get that message is the DIVERGING
part. Then I turn on other monitors to figure out what is happening in my
code. My guess is that most expert users do the same, perhaps the link to
steps or suggests for debugging would be better:

TSStep has failed due to DIVERGED_NONLINEAR_SOLVE, see <page> for
suggestions on diagnosis

Nate


On Tue, Oct 22, 2013 at 2:46 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
> On Oct 22, 2013, at 11:58 AM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
>
> > Barry Smith <bsmith at mcs.anl.gov> writes:
> >
> >> Begin forwarded message:
> >>
> >>> From: Christophe Ortiz <christophe.ortiz at ciemat.es>
> >>>
> >>> [0]PETSC ERROR:   !
> >>> [0]PETSC ERROR: TSStep has failed due to DIVERGED_NONLINEAR_SOLVE,
> increase -ts_max_snes_failures or make negative to attempt recovery!
> >>>
> >>
> >>   Do we really want this as a our "helpful message" here? Usually the
> >>   problem is a bad Jacobian etc which the person needs to track
> >>   down. It would be better if this instead listed an FAQ question
> >>   with information (and links there) to all possible causes of the
> >>   problem and how to track it down.  Just allowing failure here is
> >>   not the first step one should take I think.
> >
> > Hmm, this is not uncommon if solving a strongly nonlinear problem,
> > especially when using crude error tolerance.  So for the expert user,
> > this error is usually offering the right guidance.
>
>     What expert users do we have ?  90+% of all failures of Newton are due
> to bad Jacobians so the suggestion here is useful less than 10% of the time
> and sends all non-experts down the wrong road.
>
>    BTW: we need to finish up the refactorization of -snes_type test to the
> continuous test that runs for all solves. We have two competing fragments
> that need merging.
>
>    Barry
>
>
> >  To accommodate the
> > error-prone user, it would be fine to use a link to a web page
> > explaining the steps to debug.
>
>
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