code: @Override
      public double membership(double x) {
          if (Double.isNaN(x)) {
              return Double.NaN;
          }
          return height * 1.0 / (1.0 + Math.pow(Math.abs((x - center) / width), 2.0 * slope));
      }
docs: Computes the membership function evaluated at `x`
  
  @param x
  @return `h / (1 + \left(|x-c|/w\right)^{2s}`
  
  where `h` is the height of the Term,
  `c` is the center of the Bell,
  `w` is the width of the Bell,
  `s` is the slope of the Bell