Exponential decay model
Exponential decay model with or without a nonzero lower limit.
EXD.2(fixed = c(NA, NA), names = c("d", "e"), ...)
EXD.3(fixed = c(NA, NA, NA), names = c("c", "d", "e"), ...)fixed |
numeric vector. Specifies which parameters are fixed and at what value they are fixed. NAs for parameter that are not fixed. |
names |
vector of character strings giving the names of the parameters (should not contain ":"). The default parameter names are: init, plateau, k. |
... |
additional arguments to be passed from the convenience functions. |
The exponential decay model is a three-parameter model with mean function:
f(x) = c + (d-c)(\exp(-x/e))
The parameter init is the upper limit (attained at x=0), the parameter plateau is the lower limit reached for x going to infinity and the parameter e>0 is determining the steepness of the decay. The curve is monotonously decreasing in x.
A list of class drcMean, containing the mean function, the self starter function,
the parameter names and other components such as derivatives and a function for calculating ED values.
Christian Ritz
Organisation for Economic Co-operation and Development (OECD) (2006) Current approaches in the statistical analysis of ecotoxicity data: A guidance to application - annexes, Paris: OECD (p. 80).
## Fitting an exponential decay model ryegrass.m1<-drm(rootl~conc, data=ryegrass, fct=EXD.3()) plot(ryegrass.m1) summary(ryegrass.m1)
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