From octave-sources-request at bevo dot che dot wisc dot edu Wed Jun 18 08:18:41 2003
Subject: Re: polyfit.m patch
From: "Pascal A. Dupuis" <Pascal dot Dupuis at esat dot kuleuven dot ac dot be>
To: Paul Kienzle <pkienzle at users dot sourceforge dot net>
Cc: octave-sources at bevo dot che dot wisc dot edu
Date: Wed, 18 Jun 2003 05:58:54 -0500

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On Fri, 13 Jun 2003, Paul Kienzle wrote:

> That is not compatible with the three argument return
> option of matlab's polyfit.  Feel free to suggest alternative
> return values from wpolyfit in octave-forge which is not
> so constrained (and which already returns sigma_p).
>
In Matlab 5.3 there is a two arguments return (p and S). I've modified my
patch to return almost compatible information: the standard deviation
on p can be computed as

sqrt((S.normr/S.df)*diag(inv(S.R.'*S.R)))

matlab: S.R is a square matrix with S.df rows and columns

octave: (S.R.'*S.R) is a square matrix with S.df rows and columns

Actually, octave polyfit second argument is not compatible
with matlab 5 nor 6. The least intrusive change would be to have the
second argument being a structure, containing both the information
to compute the standard deviations as well as the fitted values, but this
would break existing programs. May be we could introduce a 'polyfitn'
(new) or 'polyfitS' (structure) in octave which is closer to matlab
behaviour ?

I know about the octave-forge solutions, but actually, on my debian,
the available octave-forge is not very up-to-date, while octave2.1 is.

Best regards

Pascal

-- 
Dr. ir. Pascal Dupuis
K. U. Leuven, ESAT/ELECTA (formerly ELEN):  http://www.esat.kuleuven.ac.be/
Kasteelpark Arenberg, 10; B-3001 Leuven-Heverlee, Belgium
Tel. +32-16-32 10 21 -- Fax +32-16-32 19 85
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