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MathGroup Archive 2004

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Re: Constraints to parameters in FindFit?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg51245] Re: [mg51200] Constraints to parameters in FindFit?
  • From: "Maxim A. Dubinnyi" <maxim at nmr.ru>
  • Date: Sun, 10 Oct 2004 01:57:16 -0400 (EDT)
  • References: <200410080654.CAA24958@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

If "Par" is always positive, write it as Par->Exp[TmpPar]
and seek for "TmpPar" instead of Par. Use Par->-Exp[TmpPar]
for negative parameters.

:)

Sincerelly,

Maxim A. Dubinnyi

Jill Foley wrote:

>Hi All,
>
>I am using FindFit to fit a series of peaks to some data. I would like 
>to be able to constrain some of the parameters of my fit to correspond 
>to physical reality. For example, some peaks should have a negative 
>amplitude, others positive, where the amplitudes are the parameters 
>that Mathematica is finding in FindFit. The peaks are all very near 
>each other, so without any constraint, it is making the wrong ones 
>negative. I'd like to specify that a given parameter should always be 
>negative. I am already giving an initial guess of the proper sign, but 
>it doesn't fix the problem.
>
>Please advise - Thanks!
>
>Jill.
>
>



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