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pdtr
Poisson distribution.SYNOPSIS:
int k;
double m, y, pdtr();
y = pdtr(k, m);
DESCRIPTION:
Returns the sum of the first k terms of the Poisson distribution:
k j
-- -m m
> e --
-- j!
j=0
The terms are not summed directly; instead the incomplete gamma integral is employed, according to the relation:
y = pdtr(k, m) = igamc(k+1, m).
The arguments must both be positive.
ACCURACY:
See igamc().