[Scilab-users] Weird error with leastsq()

[Antoine Monmayrant]

OK, forget my previous answer.

Use this:

function [n] = sellmeier(KL, lambda)
     K1 = KL(1); K2 = KL(2); K3 = KL(3);
     L1 = KL(4); L2 = KL(5); L3 = KL(6);
     lambdacarre = lambda.*lambda;
     foo1 = lambdacarre - L1;
     foo2 = lambdacarre - L2;
     foo3 = lambdacarre - L3;
     foo = 1./(foo1.*foo2.*foo3);
     n = sqrt(1 +...
     lambdacarre.*(K1*foo.*foo2.*foo3 + K2*foo.*foo1.*foo3 + 
K3*foo.*foo1.*foo2));
     n=real(n);
endfunction

Now it works.

Antoine

PS: Here is the issue: your sellmeier function should be bulletproof and 
gracefully return real values no matter what parameters you feed to it.

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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