Talk by Didrik Nielsen

You are all cordially invited to the AMLab Seminar on Thursday 3rd September at 16:00 CEST on Zoom, where ‪ Didrik Nielsen will give a talk titled “SurVAE Flows: Surjections to Bridge the Gap between VAEs and Flows”.

Paper link: https://arxiv.org/abs/2007.02731

Title: SurVAE Flows: Surjections to Bridge the Gap between VAEs and Flows

Abstract: Normalizing flows and variational autoencoders are powerful generative models that can represent complicated density functions. However, they both impose constraints on the models: Normalizing flows use bijective transformations to model densities whereas VAEs learn stochastic transformations that are non-invertible and thus typically do not provide tractable estimates of the marginal likelihood. In this paper, we introduce SurVAE Flows: A modular framework of composable transformations that encompasses VAEs and normalizing flows. SurVAE Flows bridge the gap between normalizing flows and VAEs with surjective transformations, wherein the transformations are deterministic in one direction — thereby allowing exact likelihood computation, and stochastic in the reverse direction — hence providing a lower bound on the corresponding likelihood. We show that several recently proposed methods, including dequantization and augmented normalizing flows, can be expressed as SurVAE Flows. Finally, we introduce common operations such as the max value, the absolute value, sorting and stochastic permutation as composable layers in SurVAE Flows.