docs: public void saveToFilename(String file) {
      try {
        File tgtFile = new File(file);
        BufferedWriter out = new BufferedWriter(new FileWriter(tgtFile));
        // output index first, blank delimiter, outline feature index, then weights
        labelIndex.saveToWriter(out);
        featureIndex.saveToWriter(out);
        int numLabels = labelIndex.size();
        int numFeatures = featureIndex.size();
        for (int featIndex=0; featIndex<numFeatures; featIndex++) {
          for (int labelIndex=0;labelIndex<numLabels;labelIndex++) {
            out.write(String.valueOf(featIndex));
            out.write(TEXT_SERIALIZATION_DELIMITER);
            out.write(String.valueOf(labelIndex));
            out.write(TEXT_SERIALIZATION_DELIMITER);
            out.write(String.valueOf(weight(featIndex, labelIndex)));
            out.write("\n");
          }
        }
  
        // write out thresholds: first item after blank is the number of thresholds, after is the threshold array values.
        out.write("\n");
        out.write(String.valueOf(thresholds.length));
        out.write("\n");
        for (double val : thresholds) {
          out.write(String.valueOf(val));
          out.write("\n");
        }
        out.close();
      } catch (Exception e) {
        System.err.println("Error attempting to save classifier to file="+file);
        e.printStackTrace();
      }
    }