Due to the O(|f | 3 |e| 3 ) time complexity for bi-parsing a bilingual sentence, previous studies relied on biparsing at the initialization step, and conducted Gibbs sampling by local operators (Blunsom et al., 2009;Levenberg et al., 2012) or sampling on fixed word alignments (Chung et al., 2014;Peng and Gildea, 2014).
the inference can easily result in local optimum, wherein induced derivation trees may strongly depend on the initial trees.