code: public void setThreshold(double threshold)
      {
          if(Double.isNaN(threshold) || threshold <= 0)
              throw new IllegalArgumentException("Threshold must be positive, not " + threshold);
          this.threshold = threshold;
      }
docs: Sets the threshold for a coefficient value to avoid regularization. While
  a coefficient reaches this magnitude, regularization will not be applied.
  @param threshold the coefficient regularization threshold in
  ( 0, Infinity ]