The log-logistic function — llogistic • drc

A very general way of specifying log-logistic models under various constraints on parameters.

Usage

llogistic(
  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, specifying fixed parameters (use NA for non-fixed parameters).
names: character vector of length 5, specifying the names of the parameters: b, c, d, e, f.
method: character string indicating the self starter function to use.
ssfct: a self starter function to be used.
fctName: optional character string used internally.
fctText: optional character string used internally.

Value

A list containing the nonlinear function, the self starter function, and the parameter names.

Details

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

References

Finney, D. J. (1979).

Seber, G. A. F. and Wild, C. J. (1989).

See also

LL.2, LL.3, LL.4, LL.5

Author

Christian Ritz