l4 {drc}R Documentation

The four-parameter logistic function

Description

'l4' provides the four-parameter logistic function, self starter function, names of the parameters and, optionally, first and second derivatives for a faster estimation.

Usage

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

Arguments

fixed numeric vector. Specifies which parameters are fixed and at what value they are fixed. NAs for parameter that are not fixed.
names a vector of character strings giving the names of the parameters. The default is reasonable.
useDer logical. If TRUE derivatives are supplied, if FALSE (default) they are not supplied.

Details

The four-parameter logistic function is given by the expression

f(x) = c + frac{d-c}{1+exp(b(log(x)-log(e)))}

The function is symmetric about the inflection point (e).

Value

See logistic.

Note

This function is for use with the function multdrc.

Author(s)

Christian Ritz and Jens C. Streibig

References

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

See Also

Setting c=0 yields l3. See also l5.

Examples


model1 <- multdrc(SLOPE~DOSE, CURVE, data=PestSci)
model1

rm(model1)


[Package drc version 0.9-0 Index]