vMF has been used for modeling similarity between two sentences (Guu et al., 2018), which is particularly suited to our purpose here, since we will evaluate our semantic representations in the context of modeling paraphrases (See Sections 4.1 and 4.2 for more details).
we assume q φ (y|x) follows vMF(µ α (x), κ α (x)) and the prior p θ (y) follows the uniform distribution vMF(•, 0).