Overall, our approach outperforms the three baselines, with an absolute improvement of 13 points over the extended valence grammar with posterior sparsity and 8 points over the model with universal syntactic rules.
this might be inefficient since Algorithm 1: Frank-Wolfe algorithm for t ∈ {1, ..., T } do Compute the gradient: Solve the linear program: Take the Frank-Wolfe step: it does not use the structure of the polytope and, in particular, the fact that one can easily minimize a linear function over the tree polytope using the minimum weight spanning tree algorithm.