[petsc-dev] Discussion about time-dependent optimization moved from PR

[Matthew Knepley]

On Tue, Oct 17, 2017 at 8:51 AM, Jed Brown <jed at jedbrown.org> wrote:

> Matthew Knepley <knepley at gmail.com> writes:
>
> >> It's a recipe for confusion.  Either the parameters are never passed
> >> explicitly or they are always passed explicitly and should not be stored
> >> redundantly in the context, thus perhaps enabling some sort of higher
> >> level analysis that dynamically changes parameter values.  I would go
> >> with the former for now.
> >
> >
> > I want to say again how much I dislike ad hoc memory layouts through
> > contexts and the like. We have a perfectly good layout descriptor (DM)
> > that should be used to describe data layout.
>
> This is an independent change from the adjoint work and I think it's out
> of scope right now.  If we change it, it should go in its own PR.  I
> don't like having one PR with a smattering of non-essential changes to
> old interfaces bundled together with new conventions and new
> functionality.
>

My understanding was that this discussion is not about a particular PR, but
about
the interface we should have for sensitivity and optimal control.


> Putting the parameters in a vector would enable finite differencing of
> the RHSFunction to obtain its dependence on parameters.  That might have
> high (non-scalable in number of parameters) cost, but would be less
> expensive than finite differencing an entire model.  Consider the
> scenario of 100 parameters and 1e6 state variables (at each time step).
> If we have the ability to apply the transpose of the Jacobian with
> respect to model state, we could run an adjoint simulation and only need
> 100 RHSFunction evaluations per stage, rather than 100 solves.
>

I am not sure of the point of the above paragraph. Saying the point rather
than implying
the point helps me.

   Matt

-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.caam.rice.edu/~mk51/>
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