Normalization layers are one of the key building blocks for deep neural networks. Several theoretical studies have shown that batch normalization improves the signal propagation, by avoiding the representations from becoming collinear across the layers. However, results on mean-field theory of batch normalization also conclude that this benefit comes at the expense of exploding gradients in depth. Motivated by these two aspects of batch normalization, in this study we pose the following question: "Can a batch-normalized network keep the optimal signal propagation properties, but avoid exploding gradients?" We answer this question in the affirmative by giving a particular construction of an Multi-Layer Perceptron (MLP) with linear activations and batch-normalization that provably has bounded gradients at any depth. Based on Weingarten calculus, we develop a rigorous and non-asymptotic theory for this constructed MLP that gives a precise characterization of forward signal propagation, while proving that gradients remain bounded for linearly independent input samples, which holds in most practical settings. Inspired by our theory, we also design an activation shaping scheme that empirically achieves the same properties for certain non-linear activations.

在这项研究中，我们设计了一种带有线性激活函数和批归一化的多层感知机模型，通过 Weingarten 微积分方法从理论上证明了其正向信号传播特性的精确表征，并证明了在线性独立的输入样本情况下渐近地保持梯度有界的特性。同时，我们还提出了一种激活函数塑形方案，能够在某些非线性激活函数下实现类似的特性。

趋向无深度限制的训练：无梯度爆炸的批归一化