Fast Equilibrium of SGD in Generic Situations
Authors: Zhiyuan Li,Yi Wang,Zhiren Wang
Presentation: ICLR 2024,Poster

Abstract: Normalization layers are ubiquitous in deep learning, greatly accelerating optimization. However, they also introduce many unexpected phenomena during training, for example, the Fast Equilibrium conjecture proposed by (Li et al.,2020), which states that the scale-invariant normalized network, when trained by SGD with $\eta$ learning rate and $\lambda$ weight decay, mixes to an equilibrium in $\tilde{O}(1/\eta\lambda)$ steps, as opposed to classical $e^{O(\eta^{-1})}$ mixing time. Recent works by Wang & Wang (2022); Li et al. (2022c)  proved this conjecture under different sets of assumptions. This paper aims to answer the fast equilibrium conjecture in full generality by removing the non-generic assumptions of Wang & Wang (2022); Li et al. (2022c) that the minima are isolated, that the region near minima forms a unique basin, and that the set of minima is an analytic set. Our main technical contribution is to show that with probability close to 1,  in exponential time trajectories will not escape the attracting basin containing its initial position.