Confused about the TF score when calculating CIDEr

[JJJYmmm]

In the original paper, the TF is defined as blow.

But in the code, the denominator seems to be ignored.

coco-caption/pycocoevalcap/cider/cider_scorer.py

Line 124 in 3a9afb2

vec[n][ngram] = float(term_freq)*(self.ref_len - df)