[petsc-dev] Recover from TS failure

[Mark Adams]

On Wed, Nov 1, 2017 at 8:30 PM, Jed Brown <jed at jedbrown.org> wrote:

> Mark Adams <mfadams at lbl.gov> writes:
>
> >>
> >>
> >>
> >> The last relevant output you've shown me is SNES failing a bunch of
> >> times as the adaptive controller attempts to shrink the step size and
> >> retry.  If you fixed that problem, you need to tell me.  If not, THAT is
> >> the problem you need to fix.
> >>
> >
> > That is the problem I am trying to fix.
>
> The solution to that isn't on the outside.
>

Does the "inside" exist or is there simply not a proof that it does not
exist?


>
> > Note, I am also adapting the time step when the solver converges but
> > talks a lot of iterations. Thus, no need for recovery.
>
> You can encapsulate that in an adaptive controller or put the logic (to
> get the SNES iteration number and decided whether to TSSetTimeStep) in
> the TS PostStep function.
>

That is what I do, and it is fine. It works well enough, I now am trying to
deal with TS failure.


>
> > It is the SNES failure, recover, cut time step, try again, that I am
> > working in now.
>
> That is already running in the TSAdapt.  Your failure is a result of
> something else.  Use -ts_adapt_monitor for more diagnostics about the
> controller's decisions.
>

I looked at TSAdapt for the first problem, of adapting when this look bad
but work. It failed because its algo was not quite right for this problem.
So I put a simple algo in a post step method.

Can TSAdapt deal with a SNES failure, recover, cut time step, and rerun the
step?


>
> >
> >>
> >> Did you read about -ts_error_if_step_fails on the man page
> >
> >
> > Google, and found the command line args
> >
> >
> >> for the
> >> functional interface I just cited?
> >>
> >>
> > Sorry, I missed this cite and used 'git grep' to see that it was there
> > (Matt sent me the SNES version today so I knew what to look for).
> >
> >
> >> >> but all the logic you're talking about is already in TS and
> >> >> jury-rigging it on the outside is counterproductive.  So get back to
> >> >> the root of the problem and debug why SNES is failing.
> >> >>
> >>
>
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