code: public static String format(double[][] d) {
      return d == null ? "null" : (d.length == 0) ? "[]" : //
          formatTo(new StringBuilder().append("[\n"), d, " [", "]\n", ", ", NF2).append(']').toString();
    }
docs: Formats the double array d with ',' as separator and 2 fraction digits.
  
  @param d the double array to be formatted
  @return a String representing the double array d