Four-parameter log-logistic function

A four-parameter log-logistic function.

Usage

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

l4(fixed = c(NA, NA, NA, NA), names = c("b", "c", "d", "e"), ...)

Arguments

fixed

numeric vector of length 4, specifying fixed parameters (use NA for non-fixed parameters).

names

character vector of length 4, specifying the names of the parameters (default: b, c, d, e).

...

additional arguments to llogistic.

Value

See llogistic.

Details

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

See also

LL.3, LL.5, llogistic

Author

Christian Ritz and Jens C. Streibig

Examples

spinach.m1 <- drm(SLOPE~DOSE, CURVE, data = spinach, fct = LL.4())