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

        public static double J(double x)
        {
            double ax;
            double y;
            double ans1, ans2;

            if ((ax = System.Math.Abs(x)) < 8.0)
            {
                y = x * x;
                ans1 = x * (72362614232.0 + y * (-7895059235.0 + y * (242396853.1
                    + y * (-2972611.439 + y * (15704.48260 + y * (-30.16036606))))));
                ans2 = 144725228442.0 + y * (2300535178.0 + y * (18583304.74
                    + y * (99447.43394 + y * (376.9991397 + y * 1.0))));
                return ans1 / ans2;
            }
            else
            {
                double z = 8.0 / ax;
                double xx = ax - 2.356194491;
                y = z * z;

                ans1 = 1.0 + y * (0.183105e-2 + y * (-0.3516396496e-4
                    + y * (0.2457520174e-5 + y * (-0.240337019e-6))));
                ans2 = 0.04687499995 + y * (-0.2002690873e-3
                    + y * (0.8449199096e-5 + y * (-0.88228987e-6
                    + y * 0.105787412e-6)));
                double ans = System.Math.Sqrt(0.636619772 / ax) *
                    (System.Math.Cos(xx) * ans1 - z * System.Math.Sin(xx) * ans2);
                if (x < 0.0) ans = -ans;
                return ans;
            }
        }