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Re: Constraints to parameters in FindFit?


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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