Keywords: [ Algorithms, Optimization and Computation Methods ] [ Large Scale, Parallel and Distributed ]

Abstract:
Decentralized optimization problems frequently appear in the large scale machine learning problems. However, few works work on the difficult nonconvex nonsmooth case. In this paper, we propose a decentralized primal-dual algorithm to solve this type of problem in a decentralized manner and the proposed algorithm can achieve an $\mathcal{O}(1/\epsilon^2)$ iteration complexity to attain an $\epsilon-$solution, which is the well-known lower iteration complexity bound for nonconvex optimization. To our knowledge, it is the first algorithm achieving this rate under a nonconvex, nonsmooth decentralized setting.
Furthermore, to reduce communication overhead, we also modifying our algorithm by compressing the vectors exchanged between agents.
The iteration complexity of the algorithm with compression is still $\mathcal{O}(1/\epsilon^2)$.
Besides, we apply the proposed algorithm to solve nonconvex linear regression problem and train deep learning model, both of which demonstrate the efficiency and efficacy of the proposed algorithm.

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