.TH PPOISS 3M
.SH NAME
ppoiss
.SH DESCRIPTION
function ppoiss.f

source
  Bevington, page 39.

purpose
  evaluate Poisson probability function

usage
  result = ppoiss (nobs, averag)

description of parameters
  nobs   - number of items observed
  averag - mean of distribution

subroutines and function subprograms required
  factor (n)
    calculates n factorial for integers