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MathGroup Archive 2004

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Re: Constraints to parameters in FindFit?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg51227] Re: Constraints to parameters in FindFit?
  • From: p-valko at tamu.edu (Peter Valko)
  • Date: Sat, 9 Oct 2004 04:18:43 -0400 (EDT)
  • References: <ck5e57$oio$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

For sign restiction an old trick is to use instead of paramold the
expression  Exp[paramnew] or -Exp[paramnew] in your model, and search
for paramnew (instead of paramold).

P.


Jill Foley <efoley at princeton.edu> wrote in message news:<ck5e57$oio$1 at smc.vnet.net>...
> 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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