TCT: Convexifying Federated Learning using Bootstrapped Neural Tangent Kernels
Abstract
State-of-the-art federated learning methods can perform far worse than their centralized counterparts when clients have dissimilar data distributions. For neural networks, even when centralized SGD easily finds a solution that is simultaneously performant for all clients, current federated optimization methods fail to converge to a comparable solution. We show that this performance disparity can largely be attributed to optimization challenges presented by nonconvexity. Specifically, we find that the early layers of the network do learn useful features, but the final layers fail to make use of them. That is, federated optimization applied to this non-convex problem distorts the learning of the final layers. Leveraging this observation, we propose a Train-Convexify-Train (TCT) procedure to sidestep this issue: first, learn features using off-the-shelf methods (e.g., FedAvg); then, optimize a convexified problem obtained from the network's empirical neural tangent kernel approximation. Our technique yields accuracy improvements of up to +36% on FMNIST and +37% on CIFAR10 when clients have dissimilar data.
Cite
@article{arxiv.2207.06343,
title = {TCT: Convexifying Federated Learning using Bootstrapped Neural Tangent Kernels},
author = {Yaodong Yu and Alexander Wei and Sai Praneeth Karimireddy and Yi Ma and Michael I. Jordan},
journal= {arXiv preprint arXiv:2207.06343},
year = {2022}
}
Comments
Accepted at Neural Information Processing Systems (NeurIPS) 2022. V2 releases code