The federated learning (FL) framework trains a machine learning model using decentralized data stored at edge client devices by periodically aggregating locally trained models. Popular optimization algorithms of FL use vanilla (stochastic) gradient descent for both local updates at clients and global updates at the aggregating server. Recently, adaptive optimization methods such as AdaGrad have been studied for server updates. However, the effect of using adaptive optimization methods for local updates at clients is not yet understood. We show in both theory and practice that while local adaptive methods can accelerate convergence, they can cause a non-vanishing solution bias, where the final converged solution may be different from the stationary point of the global objective function. We propose correction techniques to overcome this inconsistency and complement the local adaptive methods for FL. Extensive experiments on realistic federated training tasks show that the proposed algorithms can achieve faster convergence and higher test accuracy than the baselines without local adaptivity.

本文探讨在联邦学习中使用自适应优化方法对于本地更新的影响，指出自适应优化方法虽然可以加速模型收敛，但可能导致解决方案出现偏差，为此提出了纠正技术以克服这种不一致性，并在现实联合训练任务上进行了广泛实验，结果表明与没有局部自适应性的基线相比，所提出的算法可以实现更快的收敛和更高的测试准确性。

联邦学习中的本地适应性: 收敛和一致性