[petsc-users] TS: How to implement a simple stopping criterion

[Matthew Knepley]

On Mon, Jun 3, 2019 at 12:32 PM Patrick Sanan via petsc-users <
petsc-users at mcs.anl.gov> wrote:

> Thanks again for the pointers! Here's a quick and dirty experiment as a
> proof of concept of this,  for interest:
> https://bitbucket.org/psanan/ts_generic_rollback_example/src/master/
>
> This composes an extra "last step's state" vector with the TS object,
> overrides ts->ops->rollback, and uses a pre-step hook to keep it up to date.
>
> This allows *any* TS implementation (which doesn't already support it) to
> use TSRollBack(), which I do in a post-step hook.
>

This is cool. Why are you wrapping the Vec in a Container instead of
passing it directly?

   Matt


> Am Di., 28. Mai 2019 um 17:04 Uhr schrieb Zhang, Hong <hongzhang at anl.gov>:
>
>> You are right that TSEvent is not suitable for this case.  To stop the
>> timestepper, I would call TSSetConvergedReason(ts,TS_CONVERGED_USER) in a
>> PostStep function.
>>
>> Hong (Mr.)
>>
>> > On May 28, 2019, at 4:36 AM, Patrick Sanan via petsc-users <
>> petsc-users at mcs.anl.gov> wrote:
>> >
>> > I'm working with/on a code which uses TSSUNDIALS, and I'd like to be
>> able to stop the timestepper based on the value of the solution. In
>> particular, I wish to enforce that a given concentration has not changed by
>> more than a specified amount before stopping. Note that this is simpler
>> than general event detection, as I'm happy stopping before the condition is
>> satisfied and don't care about finding the point in time when the condition
>> is satisfied exactly.
>> >
>> > As far as I know, PETSc's event handling interface isn't supported with
>> the SUNDIALS implementation. (As an aside, I'd be happier using TSARKIMEX
>> or another native timestepper, but so far haven't been able to avoid tiny
>> timesteps).
>> >
>> > My question is whether the following approach has any obvious fatal
>> flaw, and if any TS gurus have other/better/simpler ideas.
>> >
>> > The idea is to add my own logic, say with TSSetPreStep(), to:
>> >
>> > 1. Maintain the previous step's state (this is a 1d problem, so I'm not
>> too concerned about the overhead of this)
>> > 2. Check my condition, and if it's satisfied, dump the previous step's
>> data, and use TSSetMaxTime() with the previous step's time, thus ending the
>> solve.
>> >
>>
>>

-- 
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

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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