code: @Override
      public void writeHeader(RandomAccessFile file) throws IOException {
          super.writeHeader(file);
          file.writeInt(this.k_max);
      }
docs: Writes this header to the specified file.
  Calls {@link de.lmu.ifi.dbs.elki.index.tree.TreeIndexHeader#writeHeader(java.io.RandomAccessFile)}
  and writes additionally the integer value of
  {@link #k_max}
  to the file.