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## Re: [leasqr] simple fit does not converge

**From**: |
Martijn |

**Subject**: |
Re: [leasqr] simple fit does not converge |

**Date**: |
Wed, 26 Jan 2011 11:50:51 +0100 |

Hi,
The remarks on the list made look into the data. The problem was with
the data: Ntab contained a number of NaN's.
Since this is a general help list and no bug list, I feel free to post
problems with octave forge functions as well.
Martijn
On Tue, 2011-01-25 at 23:52 +0100, Martijn wrote:
>* Hi,*
>* I am fitting a dispersion function (the Sellmeier equation) to*
>* tablulated refractive index data but leasqr.m does not converge. I am*
>* able to fit e.g. a sine to a data set, so leasqr does work.*
>* *
>* After reduction to the bare essentials my code looks like:*
>* *
>* *
>* E=0.5:.05:6;*
>* E=E(:);*
>* Ntab = sqrt(GetSopraDielFunc(E, 'bk7'));*
>* f = @(E, p) sqrt(1+p(1)./(1-p(2)*E.^2/1.54));*
>* p0 = [1.25, .011];*
>* [Nslm, p, convg, niter] = leasqr(E, Ntab, p0, f);*
>* plot(E, [Ntab, Nslm], 'linewidth', 2)*
>* *
>* The strange thing is that not only the covergence is not achieved, but p*
>* does not differ from p0, indicating something is going really wrong.*
>* *
>* The initial estimate is pretty good as can be seen by*
>* plot(E, Ntab, E, f(E, [1.25, 0.011])*
>* *
>* What's wrong here? Is it possible to show the intermediate values of p?*
>* Where is leasqrdemo gone? If I remember correctly, it did show the*
>* intermediate parameter values.*
>* *
>* Thanks,*
>* *
>* Martijn*
>* *
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