LL.4 {drc} | R Documentation |
The four-parameter log-logistic function
Description
'LL.4' and 'LL2.4' provide the four-parameter log-logistic function, self starter function, names of the parameters and, optionally, first and second derivatives for a faster estimation.
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"), ...)
LL2.4(fixed = c(NA, NA, NA, NA), names = c("b", "c", "d", "e"), ...)
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. |
... |
Additional arguments (see |
Details
The four-parameter log-logistic function is given by the expression
or in another parameterisation (converting the term into a parameter)
The function is symmetric about the inflection point ().
Value
See llogistic
.
Note
This function is for use with the function drm
.
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 yields
LL.3
. See also LL.5
.
Examples
spinach.m1 <- drm(SLOPE~DOSE, CURVE, data = spinach, fct = LL.4())
spinach.m1