The three-parameter Weibull functions
'W1.3' and W2.3 provide the three-parameter Weibull function, self starter function and names of the parameters.
'W1.3u' and 'W2.3u' provide three-parameter Weibull function where the upper limit is equal to 1, mainly for use with binomial/quantal response.
W1.3(fixed = c(NA, NA, NA), names = c("b", "d", "e"), ...)
W2.3(fixed = c(NA, NA, NA), names = c("b", "d", "e"), ...)
W2x.3(fixed = c(NA, NA, NA), names = c("d", "e", "t0"), ...)
W1.3u(upper = 1, fixed = c(NA, NA, NA), names = c("b", "c", "e"), ...)
W2.3u(upper = 1, fixed = c(NA, NA, NA), names = c("b", "c", "e"), ...)upper |
numeric value. The fixed, upper limit in the model. Default is 1. |
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 to be passed from the convenience functions. |
The three-parameter Weibull model is given by the expression
f(x) = 0 + (d-0)\exp(-\exp(b(\log(x)-e))).
The function is asymmetric about the inflection point, that is the parameter \exp(e).
The three-parameter Weibull model with upper limit 1 is given by the expression
f(x) = 0 + (1-0)\exp(-\exp(b(\log(x)-e))).
See weibull1.
This function is for use with the function drm.
Christian Ritz
## Fitting a three-parameter Weibull model ryegrass.m1 <- drm(rootl ~ conc, data = ryegrass, fct = W1.3()) ryegrass.m1
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