exppoisson.RdEstimates the two parameters of the exponential Poisson distribution by maximum likelihood estimation.
exppoisson(lrate = "loglink", lshape = "loglink",
irate = 2, ishape = 1.1, zero = NULL)Link function for the two positive parameters.
See Links for more choices.
Numeric.
Initial values for the shape and rate parameters.
Currently this function is not intelligent enough to
obtain better initial values.
The exponential Poisson distribution has density function
$$f(y; \beta = rate, \lambda = shape) =
\frac{\lambda \beta}{1 - e^{-\lambda}} \,
e^{-\lambda - \beta y + \lambda \exp{(-\beta y)}}$$
where \(y > 0\),
and the parameters shape, \(\lambda\),
and rate, \(\beta\), are positive.
The distribution implies a population facing discrete
hazard rates which are multiples of a base hazard.
This VGAM family function requires the hypergeo package
(to use their genhypergeo function).
The median is returned as the fitted value.
This VGAM family function does not work properly!
An object of class "vglmff" (see vglmff-class).
The object is used by modelling functions such as vglm
and vgam.
Kus, C., (2007). A new lifetime distribution. Computational Statistics and Data Analysis, 51, 4497–4509.
if (FALSE) { # \dontrun{
shape <- exp(1); rate <- exp(2)
rdata <- data.frame(y = rexppois(n = 1000, rate = rate, shape = shape))
library("hypergeo") # Required!
fit <- vglm(y ~ 1, exppoisson, data = rdata, trace = FALSE, maxit = 1200)
c(with(rdata, median(y)), head(fitted(fit), 1))
coef(fit, matrix = TRUE)
Coef(fit)
summary(fit)
} # }