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MathGroup Archive 2004

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Re: NonlinearFit problem

  • To: mathgroup at smc.vnet.net
  • Subject: [mg52056] Re: NonlinearFit problem
  • From: astanoff_otez_ceci at yahoo.fr (astanoff)
  • Date: Tue, 9 Nov 2004 01:36:42 -0500 (EST)
  • References: <cmnabi$7sn$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Feng-Yin Chang wrote:

> Hi All,
>    Could anyone give me any suggestion for the specified  fitting function
>    f= r^a Exp[-b r]?
>    My data point was given below,
>    data={{0, 1.00002}, {2.31507, 26.4522}, {4.32033, 56.8265}, {6.63539,
>     59.6674}, {8.64066, 39.5536}, {10.9557, 21.6862}, {12.961,
>     10.1456}, {15.276, 4.39652}}

>   The following way,
>    NonlinearFit[data,f,r,{a,b}], gives the error message,
>    FindFit::njnum:
>    The Jacobian is not a matrix of numbers at (a,b)={1.,1.}.

>   How should I do this fitting without the problem?

If you replace your first data point with {0.00001, 1.00002} it does work :
NonlinearFit[data, f, r, {a, b}]
r^5.50979/E^(0.94478*r)

v.a.
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