Message using FindFit with LevenbergMarquardt Method

*To*: mathgroup at smc.vnet.net*Subject*: [mg125454] Message using FindFit with LevenbergMarquardt Method*From*: geraldine oliveux <geraldine.oliveux at free.fr>*Date*: Wed, 14 Mar 2012 00:41:48 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com

Hello, I'm a new user of Mathematica. I'm trying to fit data to a model in which I have one parameter. I try to determine this parameter by Levenberg-Marquardt Method. I wrote the following lines : data = {{0., 0.425}, {60.6, 0.224}, {91.2, 0.1314}, {119.4, 0.0716}, {150., 0.040}, {181.8, 0.0241}} u = t*(a*sqrt[e0])/2 x = Tanh[t*(a*sqrt[e0])/2] Etac = e0*(1 - x^2) fit = FindFit[data, Etac, a, t, Method -> "LevenbergMarquardt"] But it gives me the following message : FindFit::nrlnum: "The function value {0.,-0.224+0.425\ (1. -1.\ Tanh[Times[<<2>>]]^2),-0.1314+0.425\ (1. -1.\ Tanh[Times[<<2>>]]^2),-0.0716+0.425\ (1. -1.\ Tanh[Times[<<2>>]]^2),-0.04+0.425\ (1. -1.\ Tanh[Times[<<2>>]]^2),-0.0241+0.425\ (1. -1.\ Tanh[Times[<<2>>]]^2)}\ \n is not a list of real numbers with dimensions {6} at {a} = {1.}. " What does it mean ? I think there is something I don't do well, and that it concerns the data declaration. Thank you in advance for your help, Best regards, G=E9raldine

**Follow-Ups**:**Re: Message using FindFit with LevenbergMarquardt Method***From:*Darren Glosemeyer <darreng@wolfram.com>

**Re: Message using FindFit with LevenbergMarquardt Method***From:*Bob Hanlon <hanlonr357@gmail.com>