Accord.Math.Bessel.J0 C# (CSharp) Method

        public static double J0(double x)
        {
            double ax;

            if ((ax = System.Math.Abs(x)) < 8.0)
            {
                double y = x * x;
                double ans1 = 57568490574.0 + y * (-13362590354.0 + y * (651619640.7
                    + y * (-11214424.18 + y * (77392.33017 + y * (-184.9052456)))));
                double ans2 = 57568490411.0 + y * (1029532985.0 + y * (9494680.718
                    + y * (59272.64853 + y * (267.8532712 + y * 1.0))));

                return ans1 / ans2;
            }
            else
            {
                double z = 8.0 / ax;
                double y = z * z;
                double xx = ax - 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 * 0.934935152e-7)));

                return System.Math.Sqrt(0.636619772 / ax) *
                    (System.Math.Cos(xx) * ans1 - z * System.Math.Sin(xx) * ans2);
            }
        }