Extends the class {@link DiscreteDistributionInt} for the
Poisson distribution with mean
λ >= 0. The mass function is
p(x) = e-λλx/(x!), for x = 0, 1,...
and the distribution function is
F(x) = e-λ∑j=0x λj/(j!), for x = 0, 1,....
If one has to compute
p(x) and/or
F(x) for several values of
x with the same
λ, where
λ is not too large, then it is more efficient to instantiate an object and use the non-static methods, since the functions will then be computed once and kept in arrays.
For the static methods that compute F(x) and bar(F)(x), we exploit the relationship F(x) = 1 - Gx+1(λ), where Gx+1 is the gamma distribution function with parameters (α, λ) = (x + 1, 1).