Four-parameter logistic model

A four-parameter logistic model (symmetric, with f = 1), given by $$f(x) = c + \frac{d - c}{1 + \exp(b(x - e))}$$

Usage

L.4(fixed = c(NA, NA, NA, NA), names = c("b", "c", "d", "e"), ...)

Arguments

fixed

numeric vector of length 4. Specifies which parameters are fixed and at what value they are fixed. NA indicates that the corresponding parameter is not fixed.

names

character vector of length 4 giving the names of the parameters (b, c, d, e). Default is c("b", "c", "d", "e").

...

additional arguments passed to logistic.

Value

A list of class "Boltzmann" containing the nonlinear function, self starter function, and parameter names.

See also

logistic, L.3, L.5

Examples

ryegrass.m1 <- drm(rootl ~ conc, data = ryegrass, fct = L.4())