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. https://github.com/tylin/coco-caption/blob/3a9afb2682141a03e1cdc02b0df6770d2c884f6f/pycocoevalcap/cider/cider_scorer.py#L124