2019

A Unified Theory of SGD: Variance Reduction, Sampling, Quantization and Coordinate Descent

Gorbunov, Eduard, Hanzely, Filip, Richtárik, Peter

Understand

In this paper we introduce a unified analysis of a large family of variants of proximal stochastic gradient descent ({\tt SGD}) which so far have required different intuitions, convergence analyses, have different applications, and which have been developed separately in various communities.

  • We show that our framework includes methods with and without the following tricks, and their combinations: variance reduction, importance sampling, mini-batch sampling, quantization, and coordinate sub-sampling.
  • As a by-product, we obtain the first unified theory of {\tt SGD} and randomized coordinate descent ({\tt RCD}) methods, the first unified theory of variance reduced and non-variance-reduced {\tt SGD} methods, and the first unified theory of quantized and non-quantized methods.
  • A key to our approach is a parametric assumption on the iterates and stochastic gradients.

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