• dpois(k, λ)—Returns the probability density for value k.

• ppois(k, λ)—Returns the cumulative probability distribution for value k.

• qpois(p, λ)—Returns inverse cumulative probability distribution for probability p.

• rpois(m, λ)—Returns a vector of m random numbers having the Poisson distribution.

• k is a scalar or vector of real values, k ≥ 0. To allow integration and other operations over this argument, values outside of the stated range are allowed, but they produce a 0 result.

• λ is a real mean, λ > 0.

• p is a real probability, 0 ≤ p ≤ 1.

• m is an integer, m > 0.