arXiv AI By Yunji Wang, Junjie Yao, Linyu Liu, Pinyan Lu, Zhi-Qin John Xu

Probability-Signature Dynamics: Unpacking Modular Addition Learning Within Two-Layer Networks

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The paper investigates why neural networks trained on modular addition tasks develop Fourier-structured representations that enable exact generalization. Using probability signatures, the authors show that leading gradient interactions are cyclic shift operators, which are diagonalized by the discrete Fourier transform, leading to decoupled Fourier-mode dynamics that explain Fourier sparsity, frequency matching, and phase alignment. The framework also clarifies how label noise can accelerate early loss decrease by increasing conditional label collisions, and it is demonstrated to predict frequency behavior in other operators such as XOR.

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