Description Usage Arguments Details Value Note Author(s) References See Also Examples
'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.
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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 |
The four-parameter log-logistic function is given by the expression
f(x) = c + \frac{d-c}{1+\exp(b(\log(x)-\log(e)))}
or in another parameterisation (converting the term \log(e) into a parameter)
f(x) = c + \frac{d-c}{1+\exp(b(\log(x)-\tilde{e}))}
The function is symmetric about the inflection point (e).
See llogistic
.
This function is for use with the function drm
.
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 LL.3
. See also LL.5
.
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