Accord.Math.Bessel.I0 C# (CSharp) Method

        public static double I0(double x)
        {
            double ans;
            double ax = Math.Abs(x);

            if (ax < 3.75)
            {
                double y = x / 3.75;
                y = y * y;
                ans = 1.0 + y * (3.5156229 + y * (3.0899424 + y * (1.2067492
                   + y * (0.2659732 + y * (0.360768e-1 + y * 0.45813e-2)))));
            }
            else
            {
                double y = 3.75 / ax;
                ans = (Math.Exp(ax) / Math.Sqrt(ax)) * (0.39894228 + y * (0.1328592e-1
                   + y * (0.225319e-2 + y * (-0.157565e-2 + y * (0.916281e-2
                   + y * (-0.2057706e-1 + y * (0.2635537e-1 + y * (-0.1647633e-1
                   + y * 0.392377e-2))))))));
            }

            return ans;
        }