drc (version 0.8-2)

g4: The four-parameter Gompertz function

Description

'g4' provides the four-parameter Gompertz function, self starter function and names of the parameters.

Usage

g4(names = c("b", "c", "d", "e"), useDer = FALSE)

Arguments

names

a vector of character strings giving the names of the parameters. The default is reasonable.

useDer

logical. If TRUE derivatives are supplied, otherwise they are not supplied. Not implemented!

Value

• See gompertz.

Details

The four-parameter Gompertz model is given by the expression $$f(x) = c + (d-c)\exp(-\exp(b(\log(x)-e))).$$ The function is asymmetric about the inflection point, that is the parameter $\exp(e)$.

References

Seber, G. A. F. and Wild, C. J (1989) Nonlinear Regression, New York: Wiley & Sons (pp. 330--331).

See Also

Setting $c=0$ yields g3. A more flexible function, allowing fixing or constraining parameters, is gompertz.

Examples

model1 <- multdrc(rgr~dose, pct, data=TM, fct=g4(), cm="999")
summary(model1)

rm(model1)