genpoisson {VGAM} | R Documentation |
Estimation of the two parameters of a generalized Poisson distribution.
genpoisson(llambda = "logit", ltheta = "loge", ilambda = 0.5, itheta = NULL, zero = NULL)
llambda |
Parameter link function for lambda .
See Links for more choices.
The parameter lies in the unit interval, therefore the
logit link is a reasonable default.
|
ltheta |
Parameter link function for theta .
See Links for more choices.
The parameter is positive, therefore the default is the log link.
|
ilambda |
Optional initial value for lambda . |
itheta |
Optional initial value for theta . |
zero |
An integer vector, containing the value 1 or 2. If so,
lambda or theta respectively are modelled as an intercept only.
The default value NULL means both linear/additive predictors
are modelled as functions of the explanatory variables.
|
See Consul (1989) for details.
An object of class "vglmff"
(see vglmff-class
).
The object is used by modelling functions such as vglm
,
and vgam
.
Convergence problems may occur when lambda
is very close to 0.
This distribution is useful for dispersion modelling.
T. W. Yee
Jorgensen, B. (1997) The Theory of Dispersion Models. London: Chapman & Hall
Consul, P. C. (1989) Generalized Poisson Distributions: Properties and Applications, Marcel Dekker.
y = rpois(n=100, lam=24) fit = vglm(y ~ 1, genpoisson, trace=TRUE) fitted(fit)[1:5] mean(y) summary(fit) coef(fit, matrix=TRUE) Coef(fit)