KL annealing is used to tackled the latent variable collapse issue <cite>(Bowman et al., 2016)</cite> ; VAE-CNN 4 : A variational autoencoder model with a LSTM encoder and a dilated CNN decoder (Yang et al., 2017) ; 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) .