tokens: Given this framework , many prior constructions of TPs have been proposed , such as the Dirichlet distribution in LDA , logistic normal distributions for modelling topic correlations in Correlated Topic Model ( CTM ) lafferty2006correlated , nonparametric priors like the Hierarchical Dirichlet Process teh2012hierarchical , and recently - proposed deep models like DPFA gan2015scalable , DPFM henao2015deep , and GBN zhou2016augmentable .