arXiv Machine Learning

Structured Features Overfit Where Random Features Grok

arXiv:2609. 15047v1 Announce Type: new Abstract: Xu, Vardi and Safran (ICML 2026) prove that over-parameterized ridge regression over an unstructured random Gaussian feature map groks, with the delay between memorization and generalization growing as $1/\lambda$ in the weight decay.

arXiv Machine Learning
Sep 23

A Spectral Theory of Grokking: Weight Decay induces Feature Learning

The paper presents a spectral theory explaining the phenomenon of grokking, where an initial fit to training data is followed by a delayed improvement in generalization. It shows that for homogeneous networks trained with squared loss and L₂ weight decay, residuals after memorization influence the neural tangent kernel (NTK) dynamics, leading to a transition from lazy to rich learning. The theory predicts that grokking timescales depend on the product of learning rate and weight decay, and that stronger decay can halt fitting, with empirical validation on modular addition tasks using MLPs and Transformers.

By Lenz Pracher, Pascal de Jong, Oskar Lieshaus, Alan Jeffares, Steffen Rulands
arXiv Machine Learning
Sep 23

Double Descent and Malign Overfitting in Diffusion Models

The paper investigates why diffusion models, unlike typical deep learning models, exhibit catastrophic overfitting when overparameterized. Through experiments on U‑Nets trained on CelebA and a random‑features theoretical analysis, it shows that the interpolation peak occurs at a model size proportional to the product of training samples and noise realizations, but the test loss starts to rise already at the number of samples, leading to memorization of the empirical score. Regularization techniques such as ridge penalties or early stopping can still make large models outperform smaller, unregularized ones.

By Rapha\"el Urfin, Tony Bonnaire, Giulio Biroli, Marc M\'ezard
arXiv AI
6d ago

Subspace Crystallization in Grokking: Rank Compression Tracks the Phase Transition

The paper investigates the relationship between rank compression of weight matrices and the phenomenon of grokking in neural networks. Using a mean‑field MLP and a one‑layer transformer trained on modular arithmetic, the authors find that rank compression occurs after the onset of grokking, not during memorization, and that the effective rank drops sharply around 900 steps following the grokking onset. They also observe a subspace crystallization effect, where the number of singular directions needed to preserve test accuracy shrinks dramatically during the transition, and demonstrate that artificially imposing low rank does not accelerate grokking, indicating that compression is a signature rather than a cause of the phenomenon.

By Shlok Mehendale, Paras Chopra