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Re: Leasqr matrix singular to machine precision
From: |
Dmitri A. Sergatskov |
Subject: |
Re: Leasqr matrix singular to machine precision |
Date: |
Mon, 25 Feb 2008 19:40:14 -0600 |
On Mon, Feb 25, 2008 at 3:26 PM, Archambault Fabien
<address@hidden> wrote:
> 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.
> >
> >
> > p
> >
> >
> Hi,
>
> 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).
All this should give you a clue that you are doing something wrong.
In fact your equation has only 4 independent variables (I re-wrote it
for clarity):
Y = A*( ((x1/r1)^12 -(x1/r1)^6) + ((x1/r2)^12 -(x1/r2)^6) +
B*((x2/r3)^12 - (x2/r3)^6) )
So the parameters here is A, B, x1 and x2.
Fitting this with 6 parameters will not work.
>
> --
> Fabien Archambault
Dmitri.
--
- Leasqr matrix singular to machine precision, Archambault Fabien, 2008/02/20
- Re: Leasqr matrix singular to machine precision, Archambault Fabien, 2008/02/20
- Re: Leasqr matrix singular to machine precision, Archambault Fabien, 2008/02/21
- Re: Leasqr matrix singular to machine precision, Francesco Potorti`, 2008/02/21
- Re: Leasqr matrix singular to machine precision, Archambault Fabien, 2008/02/22
- Re: Leasqr matrix singular to machine precision, Francesco Potorti`, 2008/02/22
- Re: Leasqr matrix singular to machine precision, Archambault Fabien, 2008/02/22
- Re: Leasqr matrix singular to machine precision, Przemek Klosowski, 2008/02/25
- Re: Leasqr matrix singular to machine precision, Archambault Fabien, 2008/02/25
- Re: Leasqr matrix singular to machine precision,
Dmitri A. Sergatskov <=
- Re: Leasqr matrix singular to machine precision, Archambault Fabien, 2008/02/26
- Re: Leasqr matrix singular to machine precision, Doug Stewart, 2008/02/26
- Re: Leasqr matrix singular to machine precision, Archambault Fabien, 2008/02/27
- Re: Leasqr matrix singular to machine precision, Francesco Potorti`, 2008/02/27
- Re: Leasqr matrix singular to machine precision, Rolf Fabian, 2008/02/27