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Re: Leasqr matrix singular to machine precision

From: Archambault Fabien
Subject: Re: Leasqr matrix singular to machine precision
Date: Mon, 25 Feb 2008 22:26:57 +0100
User-agent: Thunderbird (X11/20080213)

Przemek Klosowski a écrit :
For the weight on some points I thought of it but as the values I get are all of the same importance I think fitting with wt = (1) is a correct guess.

I would caution against it---every target point has its own
experimental, or systematic, or other kind of error, and those errors
are rarely the same for all points. For instance, if the points were
calculated in a counting experiment, i.e. they represent counts per
some unit of time, or are a result of a monte carlo simulation, their
error will likely be proportional to the square root of the value.



no values that are fitted are not from experimental values they are from QM calculations so each points are the "truth" (compared with MM values). In the last tests I made it was still impossible to achieve on 4 (or 6 unknown). Also the lmder (in Fortran) did not work well... And since today I tried to solve it with the nonlinear fitting of Xmgrace (constrained values are possible) and it is still not very good in fit.

Still working on it but few hope (lol).

Fabien Archambault
Equipe de dynamique des assemblages membranaires
Unité Mixte de Recherches CNRS UHP 7565
Université Henri-Poincaré, Nancy I BP 239,
54506 Vandoeuvre-lès-Nancy, cedex France

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