code: void checkRecallValidity() {
      double x0 = recall.exec(this, 0);
      for (int i = 1; i < _nBins; i++) {
        double x1 = recall.exec(this, i);
        if (x0 > x1)
          throw new H2OIllegalArgumentException(String.valueOf(i), "recall", x0 + " > " + x1);
        x0 = x1;
      }
    }
docs: Checks that recall is a non-decreasing function