public override double Function(double[] x, double[] y) { double sum = 0.0; for (int i = 0; i < x.Length; i++) { double num = x[i] - y[i]; double den = 0.5 * (x[i] + y[i]); if (den != 0) sum += (num * num) / den; } return 1.0 - sum; }