[petsc-dev] a TS feature

[Jed Brown]

Okay, who is working on this? (Is it me?) What is the timeline? Can you add
it to bitbucket issues so we can keep track? (There is a decent amount of
work incorporating it into all the methods.)


On Tue, Dec 11, 2012 at 5:42 AM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>   Right,  providing this "list of times" as a user provided function (not
> as an array of doubles) is a more general and better interface. I have no
> problem with that. (Note that one's provided function could simple access
> values in an array as appropriate :-), so Sean and my simple case are also
> supported.
>
>     Barry
>
> On Dec 10, 2012, at 11:59 PM, Shri <abhyshr at mcs.anl.gov> wrote:
>
> > I think Jed is right. Rather than giving a list of times, it is better
> to provide user-defined callback function (or functions?) for detecting the
> non-smoothness or hitting a time before ts->final_time. MATLAB Ode solvers
> call these discontinuities as 'EVENTS' and provide callback functions to
> detect them. http://www.mathworks.com/help/matlab/ref/ode23.html.
> >
> > In the power grid project that I'm involved in, there can be three
> possibilities (could be more) when the DAE integrator needs to be stopped.
> >
> > i) An exogenous event such as a random disturbance at a given
> prespecified time.
> > ii) The removal of this disturbance at another prespecified time. (only
> for analysis)
> > iii) The removal of this disturbance due to some switching (switch
> on/off) based on threshold crossing (the threshold crossing and  switching
> action could be at the same time or delayed).
> > iv) Some switching action due to abnormal conditions.
> >
> > Later on in the project, we will be passing the states from TS at the
> end of each time step to a commercial software that decides the switching
> logic and passes the switching times back to TS PostStep() interface. Thus,
> there could be a need of stopping TS based on the switching times.
> >
> > Another example of event detection is in circuit simulation where in the
> zero crossing of the waveform needs to be detected.
> >
> > I think having callback functions for 'EVENTS' would be the right
> approach.
> >
> > I recently requested for a couple of features in TS and Jed, Barry, and
> Emil kindly :) agreed
> > i) The feature of hitting the exact time has been added to the adaptive
> time-step controller and can be accessed via -ts_exact_final_time
> MATCHSTEP. Note that this is not available with methods that don't use an
> adaptive controller.
> > ii) TS can be stopped at any given time via TSPostStep() by calling
> TSSetConvergedReason() with the flag TS_CONVERGED_USER.
> >
> > Shri
> > On Mon, Dec 10, 2012 at 8:36 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> >  I'd the ability to provide to TS a list of times at which I'd like the
> ODE integrator have exactly match that time on a time-step (that is adjust
> the delta t near that time to hit it exactly).  This is something Shri
> needs.
> >
> > Is this general enough to add to the library itself? He can write an
> adaptive controller that hits any times he wants.
> >
> > As a library feature, I'd be more interested in having a controller that
> attempted to hit the zeros of a user-provided functional (because that
> could be used for other forms of model nonsmoothness).
> >
> >
>
>
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