In addition, because the sentences do not always have equal length and we do not want to penalise longer sentences, we also have three features describing the perplexity: e log(P (Tn))/length(Tn) , e log(P (Tr))/length (Tr) , and the difference between these two.
a target-side classifier, when used to identify particularly bad translation candidates, can lead to significant improvements in Bleu score.