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Re: FindFit & restricting fitting parameter

  • To: mathgroup at
  • Subject: [mg55474] Re: [mg55450] FindFit & restricting fitting parameter
  • From: "Janos D. Pinter" <jdpinter at>
  • Date: Fri, 25 Mar 2005 05:48:15 -0500 (EST)
  • References: <>
  • Sender: owner-wri-mathgroup at


FindFit and all other similar built-in model-fitting routines apply 
unconstrained local optimization methods, and hence these may miss the best 
fit even w/o constraints in nonlinear models.

You could try instead an optimization based approach: then you can flexibly 
specifiy your goodness-of-fit criterion, and also have the option to add 
arbitrary constraints regarding the parameters. The function NMinimize or 
our third party packages MathOptimizer and MathOptimizer Professional can 
be put to use in this regard.


Janos D. Pinter, PhD, DSc
PCS Inc.
E-mail: jdpinter at

At 04:41 AM 3/24/2005, Laurent Feuz wrote:

>If I want to fit some data using:
>output = FindFit[data,
>       Izero*(1 + 1/(xiPEG^2*q^2)), {{Izero, 0.12}, {xiPEG, 10}}, q]
>I can assign a starting value to my parameters (like 0.12 for Izero in
>the above case), but can I also restrict its value to a certain range
>(like 0.10<Izero<0.14)?
>Thanks for any hints!
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