code: static public double ScafferF6(double x, double y) {
      double temp1 = x * x + y * y;
      double temp2 = Math.sin(Math.sqrt(temp1));
      double temp3 = 1.0 + 0.001 * temp1;
      return (0.5 + ((temp2 * temp2 - 0.5) / (temp3 * temp3)));
    }
docs: Scaffer's F6 function