An object of class "vglmff" (see vglmff-class).
The object is used by modelling functions such as vglm
and vgam.
Details
The density function is given by
$$f(y) = \exp(-y) \times y^{shape-1} / \Gamma(shape)$$
for $shape > 0$ and $y > 0$.
Here, $\Gamma(shape)$ is the gamma
function, as in gamma.
The mean of $Y$ (returned as the fitted values)
is $\mu=shape$, and the variance is
$\sigma^2 = shape$.
References
Most standard texts on statistical distributions describe
the 1-parameter gamma distribution, e.g.,
Forbes, C., Evans, M., Hastings, N. and Peacock, B. (2011)
Statistical Distributions,
Hoboken, NJ, USA: John Wiley and Sons, Fourth edition.