Let all word vectors be normalized and $W$ be the word matrix. Inspired by BIBREF21 , where vector space models are used for evaluating topic coherence, we suggest to estimate the interpretability of $k$ th component as $ \operatorname{interp}_k W = \sum _{i,j=1}^N W_{i,k} W_{j,k} \left(W_i \cdot W_j \right). $  
 Question: How do they evaluate interpretability in this paper?
we suggest to estimate the interpretability of $k$ th component as $ \operatorname{interp}_k W = \sum _{i,j=1}^N W_{i,k} W_{j,k} \left(W_i \cdot W_j \right). $