Simple algorithms for the poisson modal cumulative probability

The paper presents and compares two new very accurate and simple pairs of approximations for the Poisson modal probability and modal cumulative probability; these have been used by Kemp and Kemp (1987, 1988) for the generation of Poisson pseudorandom variables with varying noninteger parameter by the method of one-sided search from the mode. The approximations are rational except for the square root of an integer or half-integer.