code: public static double deriv(double pred, double y, double eps)
      {
          final double x = pred - y;
          if(eps < Math.abs(x))
              return Math.signum(x);
          else
              return 0;
      }
docs: Computes the first derivative of the &epsilon;-insensitive loss
  
  @param pred the predicted value
  @param y the true value
  @param eps the epsilon tolerance
  @return the first derivative of the &epsilon;-insensitive loss