ION</h2>
<div class="codehilite"><pre><span></span><code>POIPPF(3f) computes the percent point function value at the precision
precision value P for the Poisson distribution with REAL
tail length parameter = alamba.

the poisson distribution used herein has mean = alamba and standard
deviation = sqrt(alamba). this distribution is defined for all
discrete non-negative integer x--x = 0, 1, 2, ... .

this distribution has the probability function

    f(x) = exp(-alamba) <span class="gs">* alamba*</span>*x / x