KL annealing is used to tackled the latent variable collapse issue (Bowman et al., 2016) ; VAE-CNN 4 : A variational autoencoder model with a LSTM encoder and a dilated CNN decoder<cite> (Yang et al., 2017)</cite> ; vMF-VAE 5 : A variational autoencoder model using LSTM for both encoder and decoder where the prior distribution is the von Mises-Fisher (vMF) distribution rather than a Gaussian distribution (Xu and Durrett, 2018) .