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

[Patrick Sanan]

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.

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.
> >
>
>
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