arXiv Machine Learning By Xiaoyang Li, Runni Zhou

Hard-ReLU Gradient Descent Selects an Event-Free Sensitivity Limit

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The paper investigates how exact automatic differentiation behaves under hard‑ReLU gradient descent. It shows that while gradient‑descent states converge to the piecewise‑smooth gradient flow, the derivative of the training map does not, due to missing event‑time sensitivities captured by saltation matrices. The study demonstrates that for convex objectives, activation events can create large sensitivity gaps, and provides empirical evidence that event‑aware corrections are necessary for accurate flow derivatives.

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arXiv Machine Learning
Sep 1

Singular Curvature in ReLU Training:Differentiation and the Gradient-Flow Limit Need Not Commute

The paper investigates the relationship between discrete gradient descent (GD) and its continuous-time gradient-flow counterpart in the context of ReLU neural networks. It shows that while GD states converge over a finite horizon, the exact discrete derivatives obtained via automatic differentiation do not necessarily match the derivative of the limiting flow, due to singular curvature at activation events. The authors provide a Stieltjes representation that separates continuous regional Hessians from atomic interface curvature, revealing rank-one discrepancies at activation jumps and demonstrating that even globally strongly convex residual-ReLU losses can exhibit large sensitivity ratios on certain initialization sets.

By Xiaoyang Li, Runni Zhou