Ziming Liu maps momentum-driven loss spike phase diagram in modular arithmetic training

ZimingLiu11 · x · 2026-11-01

Ziming Liu continues his thread on training spikes: they appear not only in LLM training but also in simple systems like learning modular arithmetic, which—per the slingshot mechanism paper—links spikes to grokking. He uses it as a controllable model organism.

The new finding: the momentum factors beta1 and beta2 strongly shape spiky behavior. He presents a phase diagram for modular arithmetic training and builds a toy model from quadratic loss L(x)=x². The two are qualitatively similar, but the phase boundary slopes differ sharply—about (1-β₂)∝(1-β₁)^0.92 for modular arithmetic vs 3.07 for the toy model, showing the simple picture doesn't fully capture real spiking dynamics.

Related event: KAN author Ziming Liu's new paper: loss spikes are predictable, quadratic loss picture overturned(10 posts)→

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