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