Hello,
 
I want to perform a nonlinear curve fit in order to obtain parameter
estimates from experimentally determined data (y in dependence of x),
but with an implicit function, thus, a function of which I cannot
isolate y on the left-hand side of the equation. As far as I understand,
the functions I found up to now (nls, optim) all work only for explicit
functions.
 
My data looks like
x<-c(4, 7, 10, 13, 16, 19, 22, 25, 28, 31, 34, 37, 40, 43, 46, 49, 52,
55, 58, 61)
y<-c(0.0, -0.1, 0.0, 0.1, 0.5, 0.9, 1.4, 2.3, 3.1, 3.4, 3.8, 4.2, 4.6,
4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5)

 

My function is a sigmoidal growth function based on an integrated form
of the Monod function:

 (A+B+C)*log((B+C+y)/C)-A*log((B-y)/B)=(B+C)*D*x 

 

Your ideas would be greatly appreciated. 

 

Heike Schmitt

Utrecht University

 


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