However, this assumption results in a problem for our search algorithm that begins with an empty alignment (see Algorithm 1), for which φ 0 is J and the feature value h m 3 (f, e, a) is negative infinity.
to alleviate this problem, we modify Equation B.6 slightly by adding a smoothing parameter p n ∈ (0, 1): the feature gain for Model 3 is g m 3 (f, e, a, l) = log( g n 0 ( J, φ 0 )) + where f j and e i are linked by l, φ i is the fertility before adding l, and g n 0 ( J, φ 0 ) is the gain for n 0 (φ 0 | I i=1 φ i ): Model 4 defines a new distortion sub-model D(a) that relies on word classes A and B to capture movement of phrases.