The objective is to maximize the probability of the ground truth sequence based on maximum likelihood estimation (MLE).
following loss function is minimized: where N is the number of sentence pairs in the training data, |y n | indicates the length of the n-th ground truth sentence, P n j refers to the predicted probability distribution at the j-th step for the n-th sentence, hence P n j y n j is the probability of generating the ground truth word y n j at the j-th step.