docs: public static StringBuilder formatTo(StringBuilder buf, double[][] d, String pre, String pos, String csep, NumberFormat nf) {
      if(d == null) {
        return buf.append("null");
      }
      if(d.length == 0) {
        return buf;
      }
      for(int i = 0; i < d.length; i++) {
        formatTo(buf.append(pre), d[i], csep, nf).append(pos);
      }
      return buf;
    }