Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2004
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2004

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: NonlinearFit problem

  • To: mathgroup at smc.vnet.net
  • Subject: [mg52061] Re: NonlinearFit problem
  • From: David Bailey <dave at Remove_Thisdbailey.co.uk>
  • Date: Tue, 9 Nov 2004 01:36:51 -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?
> 
> 
> Feng-Yin Chang,
> Institute of Physics,NCTU,Taiwan
> 

If you remove your first data point you get a fit. The first data point 
can't fit because the value of f[r] at r=0 can only be 0, infinity, or 
indeterminate. It would be nice if the statistics package gave a better 
diagnostic for what must be a common occurrence!

David Bailey


  • Prev by Date: Re: NonlinearFit problem
  • Next by Date: Re: Variance
  • Previous by thread: Re: NonlinearFit problem
  • Next by thread: Re: NonlinearFit problem