Accumulated Gradient Normalization

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Joeri R. Hermans, Gerasimos Spanakis, Rico Möckel ;
Proceedings of the Ninth Asian Conference on Machine Learning, PMLR 77:439-454, 2017.

Abstract

This work addresses the instability in asynchronous data parallel optimization. It does so by introducing a novel distributed optimizer which is able to efficiently optimize a centralized model under communication constraints. The optimizer achieves this by pushing a normalized sequence of first-order gradients to a parameter server. This implies that the magnitude of a worker delta is smaller compared to an accumulated gradient, and provides a better direction towards a minimum compared to first-order gradients, which in turn also forces possible implicit momentum fluctuations to be more aligned since we make the assumption that all workers contribute towards a single minima. As a result, our approach mitigates the parameter staleness problem more effectively since staleness in asynchrony induces (implicit) momentum, and achieves a better convergence rate compared to other optimizers such as asynchronous \textsceasgd and \textscdynsgd, which we show empirically.

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