expdecay {drc} | R Documentation |
Exponential decay model with a lower limit
EXD.2(fixed = c(NA, NA), names = c("plateau", "k")) EXD.3(fixed = c(NA, NA, NA), names = c("init", "plateau", "k"))
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. |
The exponential decay model is a three-parameter model with mean function:
f(x) = init + (plateau-init)(exp(-k x))
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 k (>0) is determining the steepness of the decay. Thus 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 (p. 80).
Similar models giving exponential increasing curves are AR.2
and AR.3
.
## Fitting an exponential decay model ryegrass.m1<-drm(rootl~conc, data=ryegrass, fct=EXD.3()) plot(ryegrass.m1) summary(ryegrass.m1)