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Re: fit through zero [message #52769 is a reply to message #52714]

Thu, 01 March 2007 01:38

Paolo Grigis
Messages: 171
Registered: December 2003

Senior Member

Bringfried Stecklum wrote:
> Reimar Bauer wrote:
>> Hi all
>>
>> I like to use a fit function which I can tell please go to 0,0
>>
>> How can I do that with e.g. poly_fit or did you know an equivalent routine?
>>
>> cheers
>> Reimar
>>
>>
> Hello Reimar,
>
> since you asked about poly_fit I assume that you want to fit a
> polynomial. It would be easy if poly_fit offers a keyword to flag
> certain degrees of the polynomial which then would be omitted from the
> fit. Since this is not the case I suggest to use svdfit with a user
> defined function. A polynomial without the constant term, i.e.
> y=ax+bx^2+cx^3... might be O.K.
>
> Note that svdfit uses a polynomial as well if no user-defined function
> is specified. However, the polynomial degrees cannot be flagged either.
> Since sdvfit is just a wrapper for the hardcoded nr__svdfit this feature
> can only be added by the ITT folks.
>
> with kind regards,

Here it's probably a good idea to use mpfitfun. Once you
have your polynomial function defined, it is easy to keep
some of the polynomial coefficients fixed for the fit.

Ciao,
Paolo

>
> Bringfried
>
> ------------------------------------------------------------ --------------------
> Dr. Bringfried Stecklum
> Thueringer Landessternwarte Tautenburg
> Sternwarte 5
> D-07778 Tautenburg, Germany
> Phone: +49-36427-863-54
> FAX: +49-36427-863-29
> ------------------------------------------------------------ --------------------

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[Message index]

		fit through zero By: R.Bauer on Mon, 26 February 2007 06:32
		Re: fit through zero By: Paolo Grigis on Thu, 01 March 2007 01:38
		Re: fit through zero By: Bringfried Stecklum on Thu, 01 March 2007 01:03

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