l4 {drc} | R Documentation |
'l4' provides the four-parameter logistic function, self starter function, names of the parameters and, optionally, first and second derivatives for a faster estimation.
l4(fixed = c(NA, NA, NA, NA), names = c("b", "c", "d", "e"), useDer = FALSE)
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. |
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).
See logistic
.
This function is for use with the function multdrc
.
Christian Ritz and Jens C. Streibig
Seber, G. A. F. and Wild, C. J (1989) Nonlinear Regression, New York: Wiley & Sons (p. 330).
Setting c=0 yields l3
. See also l5
.
model1 <- multdrc(SLOPE~DOSE, CURVE, data=PestSci) model1 rm(model1)