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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



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