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arXiv · 2306.02939

Improved Stability and Generalization Guarantees of the Decentralized SGD Algorithm

Batiste Le Bars·Aurélien Bellet·Marc Tommasi·Kevin Scaman·Giovanni Neglia
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Abstract

This paper presents a new generalization error analysis for Decentralized Stochastic Gradient Descent (D-SGD) based on algorithmic stability. The obtained results overhaul a series of recent works that suggested an increased instability due to decentralization and a detrimental impact of poorly-connected communication graphs on generalization. On the contrary, we show, for convex, strongly convex and non-convex functions, that D-SGD can always recover generalization bounds analogous to those of classical SGD, suggesting that the choice of graph does not matter. We then argue that this result is coming from a worst-case analysis, and we provide a refined optimization-dependent generalization bound for general convex functions. This new bound reveals that the choice of graph can in fact improve the worst-case bound in certain regimes, and that surprisingly, a poorly-connected graph can even be beneficial for generalization.

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Batiste Le Bars, Aurélien Bellet, Marc Tommasi, Kevin Scaman, Giovanni Neglia. 2024-06-13. Improved Stability and Generalization Guarantees of the Decentralized SGD Algorithm. https://arxiv.org/abs/2306.02939

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