function p = Poisson_pmf(n,L)
% p = Poisson_pmf(n,L)
% return P [ N = n events over duration t ] with return period T
% L = t/T 
%
%    Reference: http://en.wikipedia.org/wiki/Poisson_distribution

  n(find(n<0)) = 0;

  p = L.^n ./ factorial(n) * exp(-L);

% ----------------------------------------------------------------- Poisson_pmf
