We calculate the overall entropy of arc directions in a treebank conditioned on the relation type defined by the dependency label Rel and the PoS tags of the head H and the child C: Dir in (1) is the order between the child and the head in the dependency arc (Left or Right).
we compute the entropy of arc direction H for each observed tuple (rel, h, c) independently and weigh them according to the tuple frequency in the corpora.