Accord.Math.Bessel.Y0 C# (CSharp) Method

        public static double Y0(double x)
        {
            if (x < 8.0)
            {
                double y = x * x;

                double ans1 = -2957821389.0 + y * (7062834065.0 + y * (-512359803.6
                    + y * (10879881.29 + y * (-86327.92757 + y * 228.4622733))));
                double ans2 = 40076544269.0 + y * (745249964.8 + y * (7189466.438
                    + y * (47447.26470 + y * (226.1030244 + y * 1.0))));

                return (ans1 / ans2) + 0.636619772 * J0(x) * System.Math.Log(x);
            }
            else
            {
                double z = 8.0 / x;
                double y = z * z;
                double xx = x - 0.785398164;

                double ans1 = 1.0 + y * (-0.1098628627e-2 + y * (0.2734510407e-4
                    + y * (-0.2073370639e-5 + y * 0.2093887211e-6)));
                double ans2 = -0.1562499995e-1 + y * (0.1430488765e-3
                    + y * (-0.6911147651e-5 + y * (0.7621095161e-6
                    + y * (-0.934945152e-7))));
                return System.Math.Sqrt(0.636619772 / x) *
                    (System.Math.Sin(xx) * ans1 + z * System.Math.Cos(xx) * ans2);
            }
        }