The general asymmetric five-parameter logistic model

The five-parameter logistic model given by the expression $$f(x) = c + \frac{d - c}{(1 + \exp(b(x - e)))^f}$$

Usage

logistic(
  fixed = c(NA, NA, NA, NA, NA),
  names = c("b", "c", "d", "e", "f"),
  method = c("1", "2", "3", "4"),
  ssfct = NULL,
  fctName,
  fctText
)

Arguments

fixed: numeric vector of length 5. 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 5 giving the names of the parameters (b, c, d, e, f). Default is c("b", "c", "d", "e", "f").
method: character string indicating the self starter function to use ("1", "2", "3", or "4").
ssfct: a self starter function to be used. If NULL (default), a built-in self starter is selected via method.
fctName: optional character string used internally to overwrite the function name.
fctText: optional character string used internally to overwrite the description text.

Value

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

Details

This model differs from the log-logistic in that it uses x directly rather than log(x). It is sometimes referred to as the Boltzmann model.

Author

Christian Ritz

Examples

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