docs: public int getFeatureCount(double threshold, boolean useMagnitude)
    {
      int n = 0;
      for (int feat = 0; feat < weights.length; feat++) {
        for (int lab = 0; lab < weights[feat].length; lab++) {
          double thisWeight = (useMagnitude)? Math.abs(weights[feat][lab]):weights[feat][lab];
          if (thisWeight > threshold) {
            n++;
          }
        }
      }
      return n;
    }