private double getExpectedProbability(int events)
    {
        BigDecimal kFactorial = new BigDecimal(Maths.bigFactorial(events));
        double numerator = Math.exp(-mean) * Math.pow(mean, events);
        return new BigDecimal(numerator).divide(kFactorial, RoundingMode.HALF_UP).doubleValue();
    }
private double getExpectedProbability ( int events ) { BigDecimal kFactorial = new BigDecimal ( Maths . bigFactorial ( events ) ) ; double numerator = Math . exp ( - mean ) * Math . pow ( mean , events ) ; return new BigDecimal ( numerator ) . divide ( kFactorial , RoundingMode . HALF_UP ) . doubleValue ( ) ; }
This is the probability mass function
(http://en.wikipedia.org/wiki/Probability_mass_function) of
the Poisson distribution represented by this number generator.
@param events The number of occurrences to determine the
probability for.
@return The probability of the specified number of events
occurring given the current value of lamda.