“…Nowadays, the representatives include Neural Variational Document Model (NVDM) (Miao et al, 2016), Product of expert LDA (ProdLDA) (Srivastava and Sutton, 2017), and Embedded Topic Model (ETM) (Dieng et al, 2020), etc. Besides these "naive" neural variants of LDA, many other models have been investigated by applying (1) various neural modules to the topic encoder, e.g., recurrent module (Rezaee and Ferraro, 2020), attention mechanism (Li et al, 2020b), and graphical connection (Zhu et al, 2018;Yang et al, 2020), and (2) new learning paradigms, e.g., adversarial training (Wang et al, 2019), reinforcement learning (Gui et al, 2019), and lifelong learning (Gupta et al, 2020). However, despite their effectiveness on normal long texts, those models suffer from the sparsity problem of short texts (Zeng et al, 2018).…”