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MathGroup Archive 2005

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Re: NonlinearFit - Logistic Function-CalcCenter3

  • To: mathgroup at smc.vnet.net
  • Subject: [mg60489] Re: NonlinearFit - Logistic Function-CalcCenter3
  • From: Bill Rowe <readnewsciv at earthlink.net>
  • Date: Sun, 18 Sep 2005 01:15:46 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

On 9/16/05 at 3:50 AM, oddur.bjarnason at broadpark.no (Oddur
Bjarnason) wrote:


>I can fit a logistic function of the form a/(1 + b*Exp[-c*t])

>to the data points 

<data snipped>

>I can not fit the same function to the data points

<data snipped>

>I have tried to do it with Mathematica without success.

Issues like this are easier to address if you provide details of what you tried by posting the actual code you used. However,

In[14]:=
data = {{-0.08, 0.05},  {0.96, -3.19}, 
    {1.93, -6.4}, {2.98, -10.32}, {3.97, -11.8}, 
    {5.92, -13.98}, {7.88, -14.12}, {11.85, -15.34}, 
    {15.79, -14.61}, {19.7, -15.43}, {23.67, -15.83}}; 

In[15]:=
FindFit[data, a/(1 + b*Exp[(-c)*t]), {a, b, c}, t]

Out[15]=
{a -> -12.101999999839752, 
  b -> 262.91715257267236, 
  c -> 752.6850725748074}

In[16]:=
$Version
Out[16]=
"5.2 for Mac OS X (June 20, 2005)"

So, clearly it is possible to fit the curve to your data with Mathematica.
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