Exponential Poisson Distribution Family Function
Estimates the two parameters of the exponential Poisson distribution by maximum likelihood estimation.
exppoisson(lrate = "loglink", lshape = "loglink",
irate = 2, ishape = 1.1, zero = NULL)lshape, lrate |
Link function for the two positive parameters.
See |
ishape, irate |
Numeric.
Initial values for the |
zero |
The exponential Poisson distribution has density function
f(y; a = shape, b = rate) = (a*b/(1 - e^(-a))) * e^{-a - b*y + a * e^(-b*y)}
where y > 0,
and the parameters shape, a,
and rate, b, 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.
An object of class "vglmff" (see vglmff-class).
The object is used by modelling functions such as vglm
and vgam.
This VGAM family function does not work properly!
J. G. Lauder, jamesglauder@gmail.com
Kus, C., (2007). A new lifetime distribution. Computational Statistics and Data Analysis, 51, 4497–4509.
## Not run:
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)
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