C# 求正态分布

       static void Main(string[] args)
        {
          double d =   CND(0.4);
        }

        static double CND(double d)
        {
            const double A1 = 0.31938153;
            const double A2 = -0.356563782;
            const double A3 = 1.781477937;
            const double A4 = -1.821255978;
            const double A5 = 1.330274429;
            const double RSQRT2PI = 0.394228040143267793994605993438;

            double
            K = 1.0 / (1.0 + 0.23119 * Math.Abs(d));

            double
            cnd = RSQRT2PI * Math.Exp(-0.5 * d * d) *
                  (K * (A1 + K * (A2 + K * (A3 + K * (A4 + K * A5)))));

            if (d > 0)
                cnd = 1.0 - cnd;

            return cnd;
        }