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MathGroup Archive 1997

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Re: Nonlinear Fit Problem

  • To: mathgroup at smc.vnet.net
  • Subject: [mg7285] Re: Nonlinear Fit Problem
  • From: junkin <junkin at augustus0.physics.unc.edu>
  • Date: Thu, 22 May 1997 09:19:31 -0400 (EDT)
  • Organization: Duke University, Durham, NC, USA
  • Sender: owner-wri-mathgroup at wolfram.com

I have included a simple example below just to demonstrate the problems
that I have encountered with the NonlinearFit routine (in the
Statistics'NonlinearFit' package).  As you can clearly see, the addition
of a constant gives an erronious fit.  Is there a patch available, or is
this a feature that I do not understand?  I am using Mathmatica version
3.0.0.0.

Thank you,
David Junkin

In[82]:=
data7={{1,1},{2,2.1},{3,3.1},{4,4.3},{5,5.4}}

datafit=NonlinearFit[data7,
(a + 1) - 1/6 b x + 1/120 c x^2 ,{x}, {a,b,c}]

datafit2=NonlinearFit[data7,
a - 1/6 b x   1/120 c x^2 ,{x}, {a,b,c}]

Out[82]=
{{1,1},{2,2.1},{3,3.1},{4,4.3},{5,5.4}}

Out[83]=
0.9800 + 1.014285 x + 0.01428 x^2

Out[84]=
-0.01991.01428 x + 0.01428 x^2


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