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

[Stefano Zampini]

>
> It'd have to be TSAddObjective if you're building a list.  Convention is
> that Set replaces what might have been there before.
>
>
Fair enough


> In case of multiple objectives, there may be a performance reason to
> amortize evaluation of several at once, though the list interface is
> convenient.  Consider common objectives being quantities like lift and
> drag on different surfaces of a fluids simulation or stress/strain at
> certain critical joints in a structure.  Although these have some
> locality, it's reasonable to assume that state dependence will have
> quickly become global, thus make no attempt to handle sparse
> representations of the adjoint vectors lambda.
>
>
I don't get this comment. Is it related with multi-objective optimization
(e.g. Pareto)?



>
> How are parameters accessed in TSComputeRHSFunction?  It looks like
> they're coming out of the context.  Why should this be different?  (If
> parameters need to go into a Vec, we could do that, but it comes at a
> readability and possibly parallel cost if the global Vec needs to be
> communicated to local vectors.)
>
>
design paramaters are fixed troughout an adjoint/tlm run. They can be
communicated locally once at the beginning of the run.
This is what TSSetUpFromDesign and TSSetSetUpFromDesign are supposed to
handle, if I get your comment.

https://bitbucket.org/petsc/petsc/src/c2e9112e7fdfd89985f9ffc4d68b0d46cf7cad52/src/ts/interface/tspdeconstrainedutils.c?at=stefano_zampini%2Ffeature-continuousadjoint&fileviewer=file-view-default#tspdeconstrainedutils.c-579

Here is how ex23.c uses it

https://bitbucket.org/petsc/petsc/src/c2e9112e7fdfd89985f9ffc4d68b0d46cf7cad52/src/ts/examples/tutorials/ex23.c?at=stefano_zampini%2Ffeature-continuousadjoint&fileviewer=file-view-default#ex23.c-677


> > Both methods need the Jacobian of the DAE wrt the parameters: H
> > TSAdjointSetRHSJacobian(), S TSSetGradientDAE()
> >
> > Initial condition dependence on the parameters is implicitly computed in
> > Hong's code (limited to linear dependence on all the variables);
>
> How so?  Once the user gets \lambda(time=0), they can apply the chain
> rule to produce any dependency on the parameter vector?
>
>  Yes, the chain rule is implemented here

https://bitbucket.org/petsc/petsc/src/c2e9112e7fdfd89985f9ffc4d68b0d46cf7cad52/src/ts/interface/tspdeconstrainedutils.c?at=stefano_zampini%2Ffeature-continuousadjoint&fileviewer=file-view-default#tspdeconstrainedutils.c-254




-- 
Stefano
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