pdtri

Inverse Poisson distribution.

SYNOPSIS:

int k;
double m, y, pdtr();
m = pdtri(k, y);

DESCRIPTION:

Finds the Poisson variable x such that the integral from 0 to x of the Poisson density is equal to the given probability y.
This is accomplished using the inverse gamma integral function and the relation

    m = igami(k+1, y).

ACCURACY:

See the igami Help topic.

ERROR MESSAGES:

   message         condition      value returned
   domain       y < 0 or y >= 1       0.0
                     k < 0