A weighted alignment matrix<cite> (Liu et al., 2009)</cite> m is a J × I matrix to encode the probabilities of n-best alignments of the same sentence pair. Each element in the matrix stores a link probability p m (j, i), which is estimated from an n-best list by calculating relative frequencies: where Here N is an n-best list, p(a) is the probability of an alignment a in the n-best list.