[petsc-dev] BDF implementation

[Hong Zhang]

If there are state changes in the post event callback, then multistep methods would not be a good choice for the application.
I would use multistage methods such as RK type instead.

However, restarting the time stepper may still be necessary for other types of discontinuities, e.g. changes in the RHS function. 
So I would suggest to do unconditional restart at discontinuity points for safety.

Hong

> On Mar 30, 2016, at 2:49 AM, Lisandro Dalcin <dalcinl at gmail.com> wrote:
> 
> On 30 March 2016 at 02:15, Jed Brown <jed at jedbrown.org> wrote:
>> Emil Constantinescu <emconsta at mcs.anl.gov> writes:
>> 
>>> Jed had something a while back but it may have become stale. Otherwise,
>>> we had been relying on Sundials but would gladly support something native.
>> 
>> Yeah, I started a branch for LMS a few years back, but there was a lot
>> of work left before it would have been ready for general use.  I haven't
>> reviewed Lisandro's code, but it sounds like it's further along than
>> mine (and not bitrotted).
> 
> My current implementation in PetIGA was written with the limitations
> of petsc-3.6 and does not handle events.
> 
> To properly support multistep methods (and particularly BDF), I think
> we need an important additional feature in TSEvent: If the post event
> callback do change the state (i.e, there is a discontinuity in the
> solution), the timestepper has to be "restarted" (BDF implementations
> usually discard previous history and go back to order one, i.e.
> backward Euler). Would it make sense to extend the TSEvent API in such
> a way that the user can flag the timesteper about state changes?
> Otherwise, the timestepper has no other choice than unconditionally
> restart.
> 
> -- 
> Lisandro Dalcin
> ============
> Research Scientist
> Computer, Electrical and Mathematical Sciences & Engineering (CEMSE)
> Extreme Computing Research Center (ECRC)
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