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From Luc Maisonobe <Luc.Maison...@free.fr>
Subject Re: [Math] Jacobian dimensions in "AbstractLeastSquaresOptimizer"
Date Thu, 01 Sep 2011 18:36:42 GMT
Le 31/08/2011 18:09, Gilles Sadowski a écrit :
> Hello.

Hi Gilles,

>
> In the "AbstractLeastSquaresOptimizer" class (package "optimization"), there
> is (at lines 238-247):
> ---CUT---
>          jF = f.jacobian();
>          this.residuals = new double[target.length];
>
>          // Arrays shared with the other private methods.
>          point = startPoint.clone();
>          rows = target.length;
>          cols = point.length;
>
>          weightedResidualJacobian = new double[rows][cols];
>          this.weightedResiduals = new double[rows];
> ---CUT---
>
> Is it necessary to impose the layout of "jF"? Indeed, depending on the
> implementation of the "jacobian()" method, one could have
> ---CUT---
>          rows = point.length;
>          cols = target.length;
> ---CUT---
> instead. And it is not obvious from the documentation which it should be.
>
> If which data goes into which of the matrix dimensions is not important, is
> a way to specify which is which, so that both layout can be used (at the
> user's discretion)?
>
> If the layout cannot be decided by the user, it should probably stand out
> somewhere in the documentation.

In fact, I have always seen Jacobians using this layout, so from my 
point of view it was standard. I am conforted in this view by 
<http://mathworld.wolfram.com/Jacobian.html>.

So I would prefer to see improved documentation rather than providing a 
non-standard layout. I think you have already done this doc improvement 
(I am trying to read all the mails that have arrived during my 2 days 
unconnected ...)

best regards,
Luc

>
>
> Best regards,
> Gilles
>
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