numeric vector. Specifies which parameters are fixed and at what value they are fixed.
NAs for parameter that are not fixed.
names
a vector of character strings giving the names of the parameters (should not contain ":").
The order of the parameters is: c, d, delta, kappa, gamma (see under 'Details').
Value
An object containing with all components needed in multdrc.
Details
The model is given by the expression
$$f(x) = c + (d-c) ( 1 + (delta-1)\exp(-kappa(\log(x)-\log(gamma))) )^(1/(1-delta))$$
It is a five-parameter model suitable for asymmetric dose-response relationships. In fact
it is a reparameterisation of the five-parameter log-logistic model.
For delta=2 the model simplifies the four-parameter log-logistic model.
References
Seber, G. A. F. and Wild, C. J. (1989) Nonlinear Regression, New York: Wiley & Sons (pp. 332--337).