Fractional State Space Transition for Long Sequence Modeling

Abstract:State Space Models (SSMs) compress sequence history into a bounded recurrent state, making the resulting memory law a central architectural choice for long-context performance. Most modern SSMs rely on ODE-based dynamics that lead to exponential forgetting, limiting their ability to retain information over broad temporal ranges. We introduce FRAC, a selective SSM architecture derived from fractional dynamics that replaces this exponential decay with power-law long memory. To make fractional dynamics practical, FRAC approximates the heavy-tailed target kernel with a finite-state, log-spaced sum of exponential modes. This construction turns fractional memory into an efficient recurrent module with parallel training and prefill, while retaining bounded-state autoregressive decoding. Extensive experiments, including 1.3B-parameter language modeling, demonstrate that FRAC consistently improves long-context performance over state-of-the-art SSM baselines while staying competitive on short-context. These results show that fractional dynamics provide a practical and effective prior for long-context SSMs.

Machine Learning (cs.LG); Computation and Language (cs.CL)

arXiv:2609.36314 [cs.LG]

(or arXiv:2609.36314v1 [cs.LG] for this version)

https://doi.org/10.48550/arXiv.2609.36314 Focus to learn more arXiv-issued DOI via DataCite (pending registration)

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