Poisson Distribution
DESCRIPTION:
Functions for the density, cumulative distribution, quantiles and random generation of the Poisson distribution.
USAGE: 
dpois(x, lambda)
ppois(q, lambda)
qpois(p, lambda)
rpois(n, lambda)
REQUIRED ARGUMENTS:
x:
vector of (positive) quantiles. Missing values (NAs) are allowed.
q:
vector of (positive) quantiles. Missing values (NAs) are allowed.
p:
vector of probabilities. Missing values (NAs) are allowed.
n:
sample size. If length(n) is larger than 1, then length(n) random values are returned.
lambda:
vector of (positive) means.
VALUE:
density (dpois), probability (ppois), quantile (qpois), or random sample (rpois) for the Poisson distribution with mean lambda. The quantile is defined as the smallest value q such that Pr(Poisson random variate <= x) >= p.
SIDE EFFECTS:
rpois causes the creation of the dataset .Random.seed if it does not already exist, otherwise its value is updated.
DETAILS:
Elements of q or p that are missing will cause the corresponding elements of the result to be missing.
SEE ALSO:
set.seed , Binomial .
EXAMPLES: 
rpois(20,3)  #sample of size 20 with a mean of 3