about
Shattered Gradients: If resnets are the answer, then what is the question? (arxiv.org)
2 points by gwern on May 28, 2017 | hide | past | pdf | discuss on HN

In plain words: Without skip connections, gradient signals in deep networks lose their link and turn into random noise as layers stack; skip connections keep them linked. A new way to set starting weights keeps the gradient signals connected and trains very deep networks without skip connections.

Abstract · The Shattered Gradients Problem: If resnets are the answer, then what is the question?

A long-standing obstacle to progress in deep learning is the problem of vanishing and exploding gradients. Although, the problem has largely been overcome via carefully constructed initializations and batch normalization, architectures incorporating skip-connections such as highway and resnets perform much better than standard feedforward architectures despite well-chosen initialization and batch normalization. In this paper, we identify the shattered gradients problem. Specifically, we show that the correlation between gradients in standard feedforward networks decays exponentially with depth resulting in gradients that resemble white noise whereas, in contrast, the gradients in architectures with skip-connections are far more resistant to shattering, decaying sublinearly. Detailed empirical evidence is presented in support of the analysis, on both fully-connected networks and convnets. Finally, we present a new "looks linear" (LL) initialization that prevents shattering, with preliminary experiments showing the new initialization allows to train very deep networks without the addition of skip-connections.

David Balduzzi, Marcus Frean, Lennox Leary, JP Lewis, Kurt Wan-Duo Ma, Brian McWilliams
arXiv:1702.08591 · cs.NE, cs.LG, stat.ML · submitted Feb 28, 2017 · updated Jun 6, 2018
abstract · pdf · html · ICML 2017, final version

add comment on HN