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

        public static double IncompleteBeta(double aa, double bb, double xx)
        {
            double a, b, t, x, xc, w, y;
            bool flag;

            if (aa <= 0.0 || bb <= 0.0) throw new
                                            ArithmeticException("ibeta: Domain error!");

            if ((xx <= 0.0) || (xx >= 1.0))
            {
                if (xx == 0.0) return 0.0;
                if (xx == 1.0) return 1.0;
                throw new ArithmeticException("ibeta: Domain error!");
            }

            flag = false;
            if ((bb*xx) <= 1.0 && xx <= 0.95)
            {
                t = pseries(aa, bb, xx);
                return t;
            }

            w = 1.0 - xx;

            /* Reverse a and b if x is greater than the mean. */
            if (xx > (aa/(aa + bb)))
            {
                flag = true;
                a = bb;
                b = aa;
                xc = xx;
                x = w;
            }
            else
            {
                a = aa;
                b = bb;
                xc = w;
                x = xx;
            }

            if (flag && (b*x) <= 1.0 && x <= 0.95)
            {
                t = pseries(a, b, x);
                if (t <= MACHEP) t = 1.0 - MACHEP;
                else t = 1.0 - t;
                return t;
            }

            /* Choose expansion for better convergence. */
            y = x*(a + b - 2.0) - (a - 1.0);
            if (y < 0.0)
                w = incbcf(a, b, x);
            else
                w = incbd(a, b, x)/xc;

            /* Multiply w by the factor
                   a      b   _             _     _
                  x  (1-x)   | (a+b) / ( a | (a) | (b) ) .   */

            y = a * Math.Log(x);
            t = b * Math.Log(xc);
            if ((a + b) < MAXGAM && Math.Abs(y) < MAXLOG && Math.Abs(t) < MAXLOG)
            {
                t = Math.Pow(xc, b);
                t *= Math.Pow(x, a);
                t /= a;
                t *= w;
                t *= Gamma(a + b)/(Gamma(a)*Gamma(b));
                if (flag)
                {
                    if (t <= MACHEP) t = 1.0 - MACHEP;
                    else t = 1.0 - t;
                }
                return t;
            }
            /* Resort to logarithms.  */
            y += t + LogGamma(a + b) - LogGamma(a) - LogGamma(b);
            y += Math.Log(w / a);
            if (y < MINLOG)
                t = 0.0;
            else
                t = Math.Exp(y);

            if (flag)
            {
                if (t <= MACHEP) t = 1.0 - MACHEP;
                else t = 1.0 - t;
            }
            return t;
        }