logPmf
Returns the natural logarithm of the probability mass at k for this Poisson distribution.
Computed directly in log-space as k * ln(lambda) - lambda - ln(k!), avoiding overflow that would occur when computing k! or lambda^k directly for large values.
Return
the natural log of the probability mass at k. Returns Double.NEGATIVE_INFINITY when the mass is zero.
Parameters
k
the number of events at which to evaluate the log-probability.