NonlinearFit-Logistic Function-CalcCenter 3
- To: mathgroup at smc.vnet.net
- Subject: [mg60498] NonlinearFit-Logistic Function-CalcCenter 3
- From: Oddur Bjarnason <oddur.bjarnason at broadpark.no>
- Date: Sun, 18 Sep 2005 01:15:53 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
I thank Bob Hanlon and Valeri Astanoff for their prompt reply and am following their suggestions.
Purely by chance I found a solution to the problem I had using CalcCenter 3 for nonlinear fitting of data to a logistic function.
By fitting
data2={{-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}};
by NonlinearFit[data2, -a/(1 + b*Exp[-c*t]), t, {a, b, c}]
instead of
NonlinearFit[data2, a/(1 + b*Exp[-c*t]), t, {a, b, c}]
that is by changing the sign of a
I obtained the function
-14.917794621733984/(1 + 10.284628991516529*Exp[-1.0072061447043623*t]
Presumably this method can also be used in Mathematica.
I must admit that I have not as yet found out why this works.
Regards,
Oddur Bjarnason