arXiv Machine Learning
Sep 23

Unbiased Gradients, Moving Stability Boundaries: Exact Mini-Batch Geometry in Linear Self-Attention

The paper investigates how unbiased stochastic gradients affect stability in one‑layer linear self‑attention models used for in‑context linear regression. It shows that while full‑batch training preserves an elliptic stability region, mini‑batch sampling introduces batch‑dependent boundaries that drift outward, leading to an exact one‑step crossing criterion and adaptive concentration bounds. The authors also derive drift identities, prove almost‑sure escape in a balanced switching model, and analyze mode leakage and effective context length for softmax attention, corroborated by experiments on causal Transformers.

By Krishnakumar Balasubramanian
arXiv Machine Learning
Sep 4

High-Dimensional Learning Dynamics of Attention-Indexed Models

The paper investigates the training dynamics of attention mechanisms in high-dimensional settings, focusing on attention-indexed models that encompass multi-layer and multi-head architectures. It shows that while the loss landscape can be described by a finite set of trace order parameters, the online stochastic gradient descent dynamics involve an infinite hierarchy of matrix moments that can be accurately approximated by a finite truncated system. The study further reveals that the choice of attention parameterization acts as an implicit bias: untied attention can get trapped in uninformative states, whereas tied attention induces symmetry breaking and enables weak recovery with θ(d² log d) samples, and untied attention exhibits a fast-slow dynamic leading to weak recovery when symmetry is broken.

By Yizhou Xu, Margarita Sagitova, Lenka Zdeborov\'a, Florent Krzakala