Poster
CANITA: Faster Rates for Distributed Convex Optimization with Communication Compression
Zhize Li · Peter Richtarik
Virtual
Keywords: [ Optimization ] [ Federated Learning ]
Abstract:
Due to the high communication cost in distributed and federated learning, methods relying on compressed communication are becoming increasingly popular. Besides, the best theoretically and practically performing gradient-type methods invariably rely on some form of acceleration/momentum to reduce the number of communications (faster convergence), e.g., Nesterov's accelerated gradient descent [31, 32] and Adam [14]. In order to combine the benefits of communication compression and convergence acceleration, we propose a \emph{compressed and accelerated} gradient method based on ANITA [20] for distributed optimization, which we call CANITA. Our CANITA achieves the \emph{first accelerated rate} , which improves upon the state-of-the-art non-accelerated rate of DIANA [12] for distributed general convex problems, where is the target error, is the smooth parameter of the objective, is the number of machines/devices, and is the compression parameter (larger means more compression can be applied, and no compression implies ). Our results show that as long as the number of devices is large (often true in distributed/federated learning), or the compression is not very high, CANITA achieves the faster convergence rate , i.e., the number of communication rounds is (vs. achieved by previous works). As a result, CANITA enjoys the advantages of both compression (compressed communication in each round) and acceleration (much fewer communication rounds).
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