Convergence of Random Reshuffling under the Kurdyka–Łojasiewicz Inequality

Abstract

We study the random reshuffling method for smooth nonconvex optimization problems with a finite-sum structure. Though this method is widely utilized in practice, e.g., in the training of neural networks, its convergence behavior is only understood in several limited settings. In this paper, under the well-known Kurdyka–Łojasiewicz (KL) inequality, we establish strong limit-point convergence results for with appropriate diminishing step sizes; namely, the whole sequence of iterates generated by is convergent and converges to a single stationary point in an almost sure sense. In addition, we derive the corresponding rate of convergence, depending on the KL exponent and suitably selected diminishing step sizes. When the KL exponent lies in , the convergence is at a rate of with counting the number of iterations. When the KL exponent belongs to , our derived convergence rate is of the form with depending on the KL exponent. The standard KL inequality-based convergence analysis framework only applies to algorithms with a certain descent property. We conduct a novel convergence analysis for the nondescent method with diminishing step sizes based on the KL inequality, which generalizes the standard KL framework. We summarize our main steps and core ideas in an informal analysis framework, which is of independent interest. As a direct application of this framework, we establish similar strong limit-point convergence results for the reshuffled proximal point method.