Oct 5, 2026, stat.MLJ/K move · Enter open · S save
Itay Lavie, Clarissa Lauditi, Cengiz Pehlevan
John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA · Center for Brain Science, Harvard University, Cambridge, MA · Kempner Institute for the Study of Natural and Artificial Intelligence, Harvard University, Cambridge, MA
A recurring design principle in modern optimizers is to decouple update magnitude from the raw gradient norm, yet its consequences for learning-curve and resource scaling remain unclear. We isolate this mechanism by studying normalized SGD in a random-feature model with power-law teacher and data covariance. Fixed-norm updates induce an effective learning rate that grows as gradients shrink. We derive a dynamical mean-field theory (DMFT) describing the joint dependence of the loss on training time, model width and batch size. Normalization initially accelerates SGD, mapping the power-law exponent
rSGD<1 to
2rSGD/(1−rSGD), with exponential convergence at
rSGD=1 and formal finite-time convergence for
rSGD>1. At finite step size, however, the same feedback ultimately breaks the acceleration and leads to marginal stability. The late-time theory yields width-limited, edge-of-stochastic-stability (EoSS), and deterministic edge-of-stability (EoS) regimes. These phases determine when larger batches or wider models reduce serial training time at comparable compute. We quantify in which of these phases increased batch size or width can compensate the excess compute use per step by fewer optimization steps to target loss. Linearized ResNet experiments on CIFAR-5M support the predicted acceleration, breakdown, and resource-scaling trends. Together, these results connect normalization-induced acceleration, EoS effects, and width--batch allocation within a solvable theory.