(PECL stats >= 1.0.0)
stats_dens_pmf_poisson — Probability mass function of the Poisson distribution
$x, float $lb): float
Returns the probability mass at x, where the random variable
follows the Poisson distribution whose parameter is lb.
xThe value at which the probability mass is calculated
lbThe parameter of the Poisson distribution
The probability mass at x or false for failure.