arXiv Machine Learning

A Boundary-Layer Mechanism for One-Third Scaling in Online Softmax Classification

arXiv Machine Learning
Oct 23

A Fix for Softmax and Cross-Entropy

The paper identifies two numerical bugs in standard softmax, log‑softmax, and cross‑entropy implementations: Softmax Collapse, where a dominant logit causes its gradient to be rounded to zero, and Softmax Cancellation, where student and teacher logits that are equal still produce non‑zero gradients. The authors provide straightforward implementations that correct both issues. Their fix removes the previously observed "Slingshot" phenomenon, accelerates grokking with weight decay, prevents accuracy collapse without weight decay, keeps student networks aligned with teachers during distillation, and demonstrates that post‑memorization logit growth is bounded by an equilibrium between weight decay and Adam’s epsilon hyperparameter.

By Jonathan T. Barron, Dan Gnanapragasam, Michael Tschannen
arXiv Machine Learning
Oct 2

How Accurate Is Accurate Enough?

The paper investigates how the magnitude of numerical errors in a learning system should be evaluated, arguing that error impact depends on the current learning state, the class affected, and the class weight. By analyzing softmax cross‑entropy, the authors derive exact bounds on loss changes for fixed error sets and use these to provide finite‑error guarantees for losses, probabilities, predictions, and gradients. They then invert these guarantees to certify the maximum allowable primitive error for a given learning‑level requirement, demonstrating through von Mises‑Fisher learning that identical errors can have vastly different effects across states.

By Ningkang Peng, Qianfeng Yu, Jingyang Mao, Xiaoqian Peng, Yanhui Gu
arXiv AI
Sep 11

Teacher Geometry Shapes Learnability in Teacher-Student Networks

The paper investigates how the geometry of teacher neural networks affects the learnability of student networks in teacher‑student setups. By formalizing learnability as the success rate of reaching the global minimum, the authors identify two teacher distributions—one maximizing node dissimilarity (easy) and one minimizing it (hard)—that lead to markedly different success rates across various settings and activation functions. They analyze the loss landscape of small networks, revealing two types of suboptimal local minima (out‑of‑bounds and interior) whose attraction regions depend on teacher structure, and demonstrate that adjusting learning rates for the readout layer and inner biases can improve success rates. whyItMatters:"The study highlights that teacher geometry, often overlooked, plays a crucial role in determining how effectively a student network can learn, offering guidance for designing more realistic teacher‑student experiments."

By Kai J. Sandbrink, Flavio Martinelli, Alexander van Meegen, Wulfram Gerstner, Johanni Brea
arXiv Machine Learning
Sep 10

SGD in Multiclass Logistic Regression: Sequential Learning and Scaling Laws

The paper analyzes training dynamics of multiclass logistic regression on high‑dimensional Gaussian mixture models with many classes. It finds that learning proceeds sequentially from the most to the least frequent classes and, when class priors follow a power‑law, the cross‑entropy risk evolves through an initial plateau, a power‑law decay phase, and a final convergence phase. The study also shows how model capacity and optimization trade‑off under a fixed compute budget, leading to a compute‑optimal scaling law that prescribes model size and training time as functions of compute.

By Konstantinos Christopher Tsiolis, Denny Wu, Christos Thrampoulidis, Murat A. Erdogdu
arXiv Statistics ML
Oct 26

Convergence of Large-Stepsize SGD for the Cross-entropy Loss via Stochastic Lyapunov Stability

The paper presents convergence guarantees for Stochastic Gradient Descent (SGD) applied to the multiclass cross-entropy loss in both linear classifiers and two-layer neural networks. It shows that SGD dynamics can oscillate between an edge-of-stability regime dominated by curvature-driven oscillations and a stable regime where the expected loss decreases at a controlled rate. Despite these oscillations, the authors prove that SGD stabilizes the dynamics, ensuring that iterates return to stability within a fixed number of iterations and enabling convergence in the best-iterate sense even with large learning rates.

By Konstantinos Emmanouilidis, Lachlan MacDonald, Salma Tarmoun, Rene Vidal