Artemis.Engine.Maths.SpecialFunctions.IncompleteGamma C# (CSharp) Метод

        public static double IncompleteGamma(double a, double x)
        {
            double ans, ax, c, r;

            if (x <= 0 || a <= 0) return 0.0;

            if (x > 1.0 && x > a) return 1.0 - ComplementedIncompleteGamma(a, x);

            /* Compute  x**a * exp(-x) / gamma(a)  */
            ax = a * Math.Log(x) - x - LogGamma(a);
            if (ax < -MAXLOG) return (0.0);

            ax = Math.Exp(ax);

            /* power series */
            r = a;
            c = 1.0;
            ans = 1.0;

            do
            {
                r += 1.0;
                c *= x/r;
                ans += c;
            } while (c/ans > MACHEP);

            return (ans*ax/a);
        }