code: public void setSkew(double skew)
      {
          if(skew <= 0 || Double.isNaN(skew) || Double.isInfinite(skew))
              throw new IllegalArgumentException("Skew must be a positive value, not " + skew);
          this.skew = skew;
          fixCache();
      }
docs: Sets the skewness of the distribution. Lower values spread out the
  probability distribution, while higher values concentrate on the lowest
  ranks.
  
  @param skew the positive value for the distribution's skew