On the Practical Computational Power of Finite Precision RNNs for Language Recognition
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While Recurrent Neural Networks (RNNs) are famously known to be Turing complete, this relies on infinite precision in the states and unbounded computation time.We consider the case of RNNs with finite precision whose computation time is linear in the input length.Under these limitations, we show that different RNN variants have different computational power.In particular, we show that the LSTM and the Elman-RNN with ReLU activation are strictly stronger than the RNN with a squashing activation and the GRU.This is achieved because LSTMs and ReLU-RNNs can easily implement counting behavior.We show empirically that the LSTM does indeed learn to effectively use the counting mechanism.
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Transformers with O(n) decoding steps can solve any problem a Turing machine can solve in O(n) time.
“Thus, simulating an automaton (cf.Theorem 1) is not the only new capability unlocked with O(n) decoding steps: rather, such transformers can solve any problem a Turing machine can solve in O(n) time, such as simulating real-time counter machines (Weiss et al., 2018).”
From The expressive power of transformers with chain of thought (2023) · cites this paper as Weiss et al., 2018
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- Authors
- Weiss, G., Goldberg, Y., & Yahav, E.
- Affiliations
- Technion – Israel Institute of Technology (IL)
- Bar-Ilan University (IL)
- Venue
- Proceedings of the 56th Annual Meeting of the Association for Computational Linguistics (Volume 2: Short Papers)
- Published
- 2018
- Pages
- 740-745
- ISSN
- 0736-587X (ISSN-L)
- OpenAlex
- W2798579706
- Cited by
- 226
- References
- 1
- Citations by year
- 2026: 4 · 2025: 8 · 2024: 11 · 2023: 21 · 2022: 28 · 2021: 47 · 2020: 60 · 2019: 34 · 2018: 13
- FWCI
- 42.22
- Type
- conference paper
- Language
- en
- Open access
- hybrid
- doi.org
- Licence
- cc-by
- Locations
- Proceedings of the conference - Association for Computational Linguistics. Meeting (publishedVersion, cc-by)
- arXiv (Cornell University) (submittedVersion)
- arXiv (Cornell University)
- Funders
- Allen Institute for Artificial Intelligence
- European Commission
- FP7 Ideas: European Research Council (615688)
- Topics
- Physical Sciences › Computer Science › Computational Theory and Mathematics › semigroups and automata theory
- Physical Sciences › Computer Science › Artificial Intelligence › Neural Networks and Applications
- Physical Sciences › Computer Science › Computational Theory and Mathematics › Computability, Logic, AI Algorithms
- Keywords
- finite precision arithmetic, recurrent neural networks, computational power, Turing completeness, language identification, LSTM, GRU, ReLU activation, linear-time computation
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