Microsoft.Scripting.Utils.MathUtils.ErfComplement C# (CSharp) Method

        public static double ErfComplement(double v0) {
            if (v0 >= 30.0) {
                return 0.0;
            } else if (v0 <= -10.0) {
                return 2.0;
            }

            double a = Math.Abs(v0);
            if (a < 0.47) {
                return 1.0 - Erf(v0);
            }

            // Different approximations are required for different ranges of v0
            double res;
            if (a <= 4.0) {
                // Use the approximation method outlined in W. J. Cody's "Rational Chebyshev
                // Approximations for the Error Function"
                double numer = EvalPolynomial(a, ErfcNumerCoeffs);
                double denom = EvalPolynomial(a, ErfcDenomCoeffs);

                res = Math.Exp(-a * a) * numer / denom;
            } else {
                // Use the approximation method introduced by C. Tellambura and A. Annamalai
                // in "Efficient Computation of erfc(x) for Large Arguments"
                const double h = 0.5;
                const double hSquared = 0.25;
                const int nTerms = 10;
                double sq = a * a;
                res = 0.0;
                for (int i = nTerms; i > 0; i--) {
                    double term = i * i * hSquared;
                    res += Math.Exp(-term) / (term + sq);
                }

                res = h * a * Math.Exp(-sq) / Math.PI * (res * 2 + 1.0 / sq);
            }

            if (v0 < 0.0) {
                res = 2.0 - res;
            }
            return res;
        }