| 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)