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