From: <ndurand_at_fr.abx.fr>

Date: Fri 13 Jan 2006 - 19:17:19 EST

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Fri Jan 13 19:23:46 2006

Date: Fri 13 Jan 2006 - 19:17:19 EST

I made a mistake in my equations : all the logarithms are neperian!

- Réacheminé par Nadege ND Durand/RD/abx/FR le 01/13/2006 09:15 -----

Nadege ND Durand

01/12/2006 19:11

Pour : r-help@lists.R-project.org cc : Objet : Curve fitting

Hi!

I have a problem of curve fitting.

I use the following data :

- vector of predictor data :
0
0.4
0.8
1.2
1.6
- vector of response data : 0.81954 0.64592 0.51247 0.42831 0.35371

I perform parametric fits using custom equations

when I use this equation : y = yo + K *(1/(1+exp(-(a+b*ln(x))))) the
fitting result is OK

but when I use this more general equation : y = yo + K
*(1/(1+exp(-(a+b*log(x)+c*x)))) , then I get an aberrant curve!

I don't understand that... The second fitting should be at least as good as the first one because when taking c=0, both equations are identical!

There is here a mathematical phenomenon that I don't understand!....could someone help me????

Thanks a lot in advance!

Nadège

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R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Fri Jan 13 19:23:46 2006

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