“…Compared with familiar generative models, such as VAE and GAN, normalizing flows represent another generative family that has existed for a long time but only becomes popular in recent years. Normalizing flows have many types of implementation, such as planar flows [35], [36], autoregressive models [37], [38], coupling-based flows [39], [40], [41], and continuous flows [42], [43]. Dinh et al [39] introduced a coupling method to enable highly expressive transformations for flows, and this idea is further improved in [40], [41], [44].…”