Re: NonlinearFit problem

*To*: mathgroup at smc.vnet.net*Subject*: [mg52051] Re: NonlinearFit problem*From*: Antti Penttilä@smc.vnet.net*Date*: Tue, 9 Nov 2004 01:36:35 -0500 (EST)*Organization*: University of Helsinki*References*: <cmnabi$7sn$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

The algorithm uses model's first or second derivatives, and in your case the partial derivative in respect to a is not numerical at r=0 because the Log[r]-function. D[ r^a Exp[-b r], a] = e^(-b r) r^a Log[r] and D[ r^a Exp[-b r], {a, 2}] = e^(-b r) r^a Log[r]^2 If you change your first datapoint to something like {0.0000001, 1.00002} instead of {0, 1.00002} the fit has no problems. -- Antti Penttilä Antti.I.Penttila at helsinki.fi.removethis Researcher Observatory tel. +358 50 5240968 00014 University of Helsinki