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

[Zhang, Hong]

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.
>