[petsc-dev] TSSolve web page JED and EMIL READ THIS!

[Dmitry Karpeyev]

Hong, I could stop by your office tomorrow to chat a bit more about the
"funky system" I'm talking about.
Is tomorrow good for you?
Dmitry.

On Wed Feb 11 2015 at 8:30:47 PM Hong Zhang <hongzhang at anl.gov> wrote:

> This is a good heads-up for me. Actually I wanted that our adjoint models
> could handle forward integrations like this:
> TSSolve(ts,u);
> TSStep(ts);
> TSSolve(ts,u);
>
> Then the reverse run would look like:
> TSAdjointSolve(ts);
> TSAdjointStep(ts);
> TSAdjointSolve(ts);
>
> This flexibility should be very useful for “funky systems”.
>
> On Feb 8, 2015, at 8:41 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>
> >
> >  If the number of degrees of freedom do not change and they have
> essentially the same "meaning" regardless of which process they are on then
> we can "hide" inside the Vec object (and Mat object) the fact that they
> move around between processors so TS shouldn't care.
> >
> >  BUT note that if the user manages the calling of TSStep() themselves
> then the user has to similarly manage calling the TSAdjointStep() stuff
> correctly themselves backwards. And if they are ad hoc combining TSStep()
> for the field with some "push particle" crap for the particles then likely
> all the TSAdjoint stuff goes out the window. Hence my desire for TS to
> treat the entire field+particle stuff as one "big old" set of ODEs so users
> get all the good stuff (like Adjoints and proper coupled error control) for
> free.
> >
> >
> >
> >
> >> On Feb 8, 2015, at 8:29 PM, Dmitry Karpeyev <karpeev at mcs.anl.gov>
> wrote:
> >>
> >> This is a bit off-topic, but I'm dealing exactly with this sort of
> "funky system" -- particles+field.
> >> Since degrees of freedom do move between processors, it's unclear how
> it fits into the current
> >> TS framework short of rebuilding the TS every timestep. That's a bit
> inconvenient, since now I
> >> have to do my own error and timestep size control etc.  It might be too
> late to do anything about
> >> TS to help this, but I'm also hoping to use TSAdjoint with this system,
> so it may be good -- before
> >> TSAdjoint becomes to rigidly entrenched -- to think about how to
> accommodate these systems.
> >>
> >> On Sun Feb 08 2015 at 8:16:30 PM Barry Smith <bsmith at mcs.anl.gov>
> wrote:
> >>
> >>> On Feb 8, 2015, at 8:11 PM, Jed Brown <jed at jedbrown.org> wrote:
> >>>
> >>> Barry Smith <bsmith at mcs.anl.gov> writes:
> >>>>  Why can't TS handle that? Users always prefer to use the lowest
> >>>>  level thing available, that doesn't mean it is right.
> >>>>
> >>>>  In the language of TS what does a "funky system, liked mixed
> >>>>  particle-field," mean, does it require a little more API on our
> >>>>  side? I'm much rather have Emil and Jed control the time-stepping
> >>>>  then some ignorant user.
> >>>
> >>> Dofs move to different processes at each stage.  That isn't compatible
> >>> with Vec.  Do we need to overhaul Vec before users can integrate such a
> >>> system?
> >>
> >>   Well eventually.
> >>>
> >>> Practicality wins over purity.
> >>
> >>  I never said remove TSStep() or make it completely private. I just
> want to limit its use to when it is really needed by the user.
> >>
> >>
> >
>
>
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