[Scilab-users] Weird error with leastsq()

[Antoine Monmayrant]

Hello,

I can tell you what happened: for some values of lambda and some values 
of K(4,5,6), your function is undefined and the leastsq goes kaboom!

It is never a good idea to fit a function that can become undefined for 
some parameters/xvalues.
Try to redefine the function you fit to avoid any undefined values.

Antoine

I was able to use the range [1:51], but not  [1:52].

Le 27/08/2020 à 16:52, Dang Ngoc Chan, Christophe a écrit :
> Hello all,
>
> Let's talk about optics.
> I have a glass, its refraction index n varies with the wavelength lamba.
> I have a CSV file with the corresponding data (verre_HOQ.cvs attached), 52 points.
>
> I want to model this with the Sellmeier model
> https://en.wikipedia.org/wiki/Sellmeier_equation
> and use for this the attached script (regression_sellmeier.sce).
>
> Mind to set the path at line 7 of the script if you want to run it.
>
> My problem:
> I can run piecewise regression,
> i.e. it runs when I work with the points 1 to 25, 13 to 39, or 32 to 52;
> e.g. at lines 11 and 12, it works when I use
>
> // ----------
>
> lambda = 1e-3*donnees(1:25, 1); // en µm
>
> nexp = donnees(1:25, 2);
>
> // ----------
>
> but when I try to extend these ranges (and of course when I try to use all the points),
> it fails with the following error:
>
> 5215700pt: Wrong type for output argument #1: Real scalar expected.
>
> Can anyone tell me what goes on here?
>
> Regards
>
> --
> Christophe Dang Ngoc Chan
> Mechanical calculation engineer
>
>
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