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NonlinearFit - Logistic Function-CalcCenter3


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

to the data points -0.06 -0.05 
      0.97 -4.2 
      1.99 -9.79 
      3 -12.44 
      3.99 -14.57 
      5.92 -16.85 
      7.87 -17.27 
      11.89 -17.69 
      15.8 -17.74 
      19.74 -17.77 
      23.67 -18.19 


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


I have tried to do it with Mathematica without success.

I have no problem when I use a progam called CurveExpert.

Regards, Oddur Bjarnason



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