In particular, the memory network Chien and Lin, 2018) , neural variational learning (<cite>Serban et al., 2017</cite>; Chung et al., 2015) , neural discrete representation (Jang et al., 2016; Maddison et al., 2016; van den Oord et al., 2017) , recurrent ladder network (Rasmus et al., 2015; Prémont-Schwarz et al., 2017; Sønderby et al., 2016) , stochastic neural network (Fraccaro et al., 2016; Goyal et al., 2017; Shabanian et al., 2017) , Markov recurrent neural network (Venkatraman et al., 2017; Kuo and Chien, 2018) , sequence GAN (Yu et al., 2017) and reinforcement learning (Tegho et al., 2017) are introduced in various deep models which open a window to more practical tasks, e.g. reading comprehension, sentence generation, dialogue system, question answering and machine translation.