Softmax loss is a loss that is similar to the zero-one loss, but directly defines a probabilistic model and attempts to maximize the probability of the oracle translations (Berger, Della Pietra, and Della Pietra 1996;Och and Ney 2002;Blunsom, Cohn, and Osborne 2008).
if we assume that MT is modeled according to the log-linear model we can define softmax loss softmax (•) as follows: From Equation 21we can see that only the oracle translations contribute to the numerator, and all candidates in c (i) contributes to the denominator.