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Supplying gradient for the subset of parameters

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zym
zym el 11 de Ag. de 2022
Comentada: Bruno Luong el 11 de Ag. de 2022
Hi, I would like to ask if it is possible to supply analytical gradient for some parameters when optimising, using let's say fmincon. Support pages as well as documentation provide examples where user specifies analytical gradient for every parameter over which some function is optimised. In my problem, it is likely that analytical gradients are easy just for some parameters, therefore, I would like to help the optimisation by including this information and then rely on optimisation toolboxes to compute gradients for other parameters.
I may have a simple questions but I could not find the answer to.
Appreciate your help

Respuesta aceptada

Alan Weiss
Alan Weiss el 11 de Ag. de 2022
The short answer is no: there is no provision to provide analytic gradients for a subset of the parameters. I cannot think of a workaround, either.
Alan Weiss
MATLAB mathematical toolbox documentation
  1 comentario
zym
zym el 11 de Ag. de 2022
Editada: zym el 11 de Ag. de 2022
Thanks a lot for the prompt response. I happenned to get stuck on this problem for the maximum likelihood estimation.
For the MLE I am using kalman filter to obtain loglikelihood. The likelihood with Kalman filter tends to not have an easy expression for the gradient as disccused by Durbin and Koopman "Time series analysis by state space methods" p.180. Authors argue that using gradients approximated using numerical methods maybe more efficient for some parameters though not for all.

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Bruno Luong
Bruno Luong el 11 de Ag. de 2022
May be you could provide the gradient interface for all, but compute the subset derivative analytically and the complement by finite difference, providing you know ho to chose the step size (which might not be trivial).
  2 comentarios
zym
zym el 11 de Ag. de 2022
If I understand correctly, you are suggesting to compute the numerical gradient for parameters which do not have the analytical expression. Yes that is a sort of a solution. It would be just nice to call matlab's toolboxes for that. Thanks!
Bruno Luong
Bruno Luong el 11 de Ag. de 2022
Yes, that's the idea.

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