Invertible DenseNets with Concatenated LipSwish

Yura Perugachi-Diaz, Jakub Mikolaj Tomczak, Sandjai Bhulai

Keywords: invertible, densenets, normalizing flow

TL;DR: Invertible DenseNets: An extension of Residual Flows based on the Lipschitz continuity of concatenation and CLipSwish activation functions.

Abstract: We introduce Invertible Dense Networks (i-DenseNets), a more parameter efficient extension of Residual Flows. The method relies on an analysis of the Lipschitz continuity of the concatenation in DenseNets, where we enforce invertibility of the network by satisfying the Lipschitz constant. Furthermore, we propose a learnable weighted concatenation, which not only improves the model performance but also indicates the importance of the concatenated weighted representation. Additionally, we introduce the Concatenated LipSwish as activation function, for which we show how to enforce the Lipschitz condition and which boosts performance. The new architecture, i-DenseNet, out-performs Residual Flow and other flow-based models on density estimation evaluated in bits per dimension, where we utilize an equal parameter budget. Moreover, we show that the proposed model out-performs Residual Flows when trained as a hybrid model where the model is both a generative and a discriminative model.

Code Of Conduct: I certify that all co-authors of this work have read and commit to adhering to the NeurIPS Statement on Ethics, Fairness, Inclusivity, and Code of Conduct.

Code: https://github.com/yperugachidiaz/invertible_densenets

Community Implementations: [ 1 code implementation](https://www.catalyzex.com/paper/arxiv:2102.02694/code)