numeric vector specifying which parameters are fixed and at what value they are fixed.
NAs are used for parameters that are not fixed.
names
a vector of character strings giving the names of the parameters (should not contain ":").
The default is reasonable (see under 'Usage').
fctName
optional character string used internally by convenience functions.
fctText
optional character string used internally by convenience functions.
Value
The value returned is a list containing the nonlinear function, the self starter function
and the parameter names.
Details
Following Groot et al (1996) the two-phase model function is defined as follows
$$f(x) = c + \frac{d1-c}{1+\exp(b1(\log(x)-\log(e1)))} + \frac{d2}{1+\exp(b2(\log(x)-\log(e2)))}$$
For each of the two phases, the parameters have the same interpretation as in the ordinary log-logistic
model.
References
Groot, J. C. J., Cone, J. W., Williams, B. A., Debersaques, F. M. A., Lantinga, E. A. (1996)
Multiphasic analysis of gas production kinetics for in vitro fermentation of ruminant feeds,
Animal Feed Science Technology, 64, 77--89.
See Also
The basic component in the two-phase model is the log-logistic model
llogistic.