The input of the neural rule selection model is a vector representation fort, another vector representation forẽ, and a set of ξ vector representations for both source-side and target-side context words of r: In our model, C (r) is calculated differently depending on the number of nonterminals included in the rule.
equation 7 defines C out (r, n) to be context words (n-grams) around r and C in (r, n, X k ) to be boundary words (n-grams) covered by nonterminal X k in r. 1 The context words used for a translation rule r with K nonterminals are shown as below.