[petsc-dev] a TS feature

[Barry Smith]

  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).
> 
>