Luckily, we can exploit the structure of the problem to efficiently compute the partition function, where T (u) is the set of all trees under the grammar that have yield u.
similarly, Adaptor Grammars (Johnson et al., 2006), a non-parametric Bayesian generalization of PCFGs, have been applied to the unsupervised version of the task (Botha and Blunsom, 2013;sirts and Goldwater, 2013).