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MathGroup Archive 2001

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Getting parameters from Fit[]..

  • To: mathgroup at smc.vnet.net
  • Subject: [mg27055] Getting parameters from Fit[]..
  • From: "Mark Harder" <harderm at ucs.orst.edu>
  • Date: Sat, 3 Feb 2001 04:58:52 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

    I am doing a linear fit to obtain parameters for use in a larger, 
iterative procedure (a separable linear-nonlinear data fitting 
algorithm), and I'm trying to use Fit[] to do this.  Unfortunately, Fit 
does not return parameters by themselves, just the linear combination of 
my basis functions(which are much more complicated than the usual 
examples given in the documentation) weighted by the parameters.  I have 
tried various things, like using Regress instead of Fit, but that prints 
out at least a written report of the parameters every time it is 
invoked, which will make for a very cluttered output when included in 
the larger problem I am trying to solve.  I suppose I can find a method 
to isolate just the parts of the output of Fit that contain the 
parameters and process them to get the parameters, but that seems 
awkward and might introduce numerical errors.  I've looked at the 
MathGroup archives and found only 1 response to this question in the 
past, which was "Sorry, dont know how to do that. why don't you use 
Regress?".
    Doesn't Mathematica provide any simple method for recovering just 
the parameter vector from a linear fit?  If it doesn't, perhaps it ought 
to.  Alternatively, is there some way to get Regress to provide the 
BestFitParameters rules without printing them out?  Or, is there some 
*simple* and accurate way of getting the parameters from the Fit output 
as is?
-mark harder
harderm at ucs.orst.edu


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