Batch Normalization (BN) is a commonly used technique to accelerate and stabilize training of deep neural networks. Despite its empirical success, a full theoretical understanding of BN is yet to be developed. In this work, we analyze BN through the lens of convex optimization. We introduce an analytic framework based on convex duality to obtain exact convex representations of weight-decay regularized ReLU networks with BN, which can be trained in polynomial-time. Our analyses also show that optimal layer weights can be obtained as simple closed-form formulas in the high-dimensional and/or overparameterized regimes. Furthermore, we find that Gradient Descent provides an algorithmic bias effect on the standard non-convex BN network, and we design an approach to explicitly encode this implicit regularization into the convex objective. Experiments with CIFAR image classification highlight the effectiveness of this explicit regularization for mimicking and substantially improving the performance of standard BN networks.

本文通过凸优化的视角分析Batch Normalization，提出了一个基于凸对偶的解析框架，可以精确地描述用Batch Normalization训练的带有权重衰减的ReLU网络，并证明在高维和过参数化情况下，理论上可以获得一些简单的解析的最优层权重和可训练的凸约束优化问题，并发现梯度下降给标准的非凸BN网络提供了算法偏差效应，通过我们的方法可以将这种隐式正则化显性编码到凸目标中，实验结果表明该方法可以模拟和显著提高标准BN网络的性能。

ReLU网络中批归一化的解析：等价的凸优化模型与隐式正则化