On the Expressivity of Recurrent Neural Cascades with Identity

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Auteurs principaux: Knorozova, Nadezda Alexandrovna, Ronca, Alessandro
Format: Preprint
Publié: 2024
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author Knorozova, Nadezda Alexandrovna
Ronca, Alessandro
author_facet Knorozova, Nadezda Alexandrovna
Ronca, Alessandro
contents Recurrent Neural Cascades (RNC) are the class of recurrent neural networks with no cyclic dependencies among recurrent neurons. Their subclass RNC+ with positive recurrent weights has been shown to be closely connected to the star-free regular languages, which are the expressivity of many well-established temporal logics. The existing expressivity results show that the regular languages captured by RNC+ are the star-free ones, and they leave open the possibility that RNC+ may capture languages beyond regular. We exclude this possibility for languages that include an identity element, i.e., an input that can occur an arbitrary number of times without affecting the output. Namely, in the presence of an identity element, we show that the languages captured by RNC+ are exactly the star-free regular languages. Identity elements are ubiquitous in temporal patterns, and hence our results apply to a large number of applications. The implications of our results go beyond expressivity. At their core, we establish a close structural correspondence between RNC+ and semiautomata cascades, showing that every neuron can be equivalently captured by a three-state semiautomaton. A notable consequence of this result is that RNC+ are no more succinct than cascades of three-state semiautomata.
format Preprint
id arxiv_https___arxiv_org_abs_2405_11657
institution arXiv
publishDate 2024
record_format arxiv
spellingShingle On the Expressivity of Recurrent Neural Cascades with Identity
Knorozova, Nadezda Alexandrovna
Ronca, Alessandro
Machine Learning
Artificial Intelligence
Formal Languages and Automata Theory
Logic in Computer Science
Neural and Evolutionary Computing
Recurrent Neural Cascades (RNC) are the class of recurrent neural networks with no cyclic dependencies among recurrent neurons. Their subclass RNC+ with positive recurrent weights has been shown to be closely connected to the star-free regular languages, which are the expressivity of many well-established temporal logics. The existing expressivity results show that the regular languages captured by RNC+ are the star-free ones, and they leave open the possibility that RNC+ may capture languages beyond regular. We exclude this possibility for languages that include an identity element, i.e., an input that can occur an arbitrary number of times without affecting the output. Namely, in the presence of an identity element, we show that the languages captured by RNC+ are exactly the star-free regular languages. Identity elements are ubiquitous in temporal patterns, and hence our results apply to a large number of applications. The implications of our results go beyond expressivity. At their core, we establish a close structural correspondence between RNC+ and semiautomata cascades, showing that every neuron can be equivalently captured by a three-state semiautomaton. A notable consequence of this result is that RNC+ are no more succinct than cascades of three-state semiautomata.
title On the Expressivity of Recurrent Neural Cascades with Identity
topic Machine Learning
Artificial Intelligence
Formal Languages and Automata Theory
Logic in Computer Science
Neural and Evolutionary Computing
url https://arxiv.org/abs/2405.11657