Re: Message using FindFit with LevenbergMarquardt Method

*To*: mathgroup at smc.vnet.net*Subject*: [mg125467] Re: Message using FindFit with LevenbergMarquardt Method*From*: "Oleksandr Rasputinov" <oleksandr_rasputinov at ymail.com>*Date*: Thu, 15 Mar 2012 00:25:44 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <jjpbao$p9l$1@smc.vnet.net>

On Wed, 14 Mar 2012 05:46:00 -0000, geraldine oliveux <geraldine.oliveux at free.fr> wrote: > 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 > sqrt should be Sqrt, and you need to include e0 as a parameter (unless you know a value for it, in which case you should specify that). 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, e0}, t, Method -> "LevenbergMarquardt"]