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Hauptverfasser: Morgan, Alexander, Khan, Ummay Sumaya, Liu, Lingjia, Zheng, Lizhong
Format: Preprint
Veröffentlicht: 2026
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Online-Zugang:https://arxiv.org/abs/2602.21454
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author Morgan, Alexander
Khan, Ummay Sumaya
Liu, Lingjia
Zheng, Lizhong
author_facet Morgan, Alexander
Khan, Ummay Sumaya
Liu, Lingjia
Zheng, Lizhong
contents Recurrent neural networks (RNNs) can be interpreted as discrete-time state-space models, where the state evolution corresponds to an infinite-impulse-response (IIR) filtering operation governed by both feedforward weights and recurrent poles. While, in principle, all parameters including pole locations can be optimized via backpropagation through time (BPTT), such joint learning incurs substantial computational overhead and is often impractical for applications with limited training data. Echo state networks (ESNs) mitigate this limitation by fixing the recurrent dynamics and training only a linear readout, enabling efficient and stable online adaptation. In this work, we analytically and empirically examine why learning recurrent poles does not provide tangible benefits in data-constrained, real-time learning scenarios. Our analysis shows that pole learning renders the weight optimization problem highly non-convex, requiring significantly more training samples and iterations for gradient-based methods to converge to meaningful solutions. Empirically, we observe that for complex-valued data, gradient descent frequently exhibits prolonged plateaus, and advanced optimizers offer limited improvement. In contrast, fixed-pole architectures induce stable and well-conditioned state representations even with limited training data. Numerical results demonstrate that fixed-pole networks achieve superior performance with lower training complexity, making them more suitable for online real-time tasks.
format Preprint
id arxiv_https___arxiv_org_abs_2602_21454
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle When Learning Hurts: Fixed-Pole RNN for Real-Time Online Training
Morgan, Alexander
Khan, Ummay Sumaya
Liu, Lingjia
Zheng, Lizhong
Machine Learning
Recurrent neural networks (RNNs) can be interpreted as discrete-time state-space models, where the state evolution corresponds to an infinite-impulse-response (IIR) filtering operation governed by both feedforward weights and recurrent poles. While, in principle, all parameters including pole locations can be optimized via backpropagation through time (BPTT), such joint learning incurs substantial computational overhead and is often impractical for applications with limited training data. Echo state networks (ESNs) mitigate this limitation by fixing the recurrent dynamics and training only a linear readout, enabling efficient and stable online adaptation. In this work, we analytically and empirically examine why learning recurrent poles does not provide tangible benefits in data-constrained, real-time learning scenarios. Our analysis shows that pole learning renders the weight optimization problem highly non-convex, requiring significantly more training samples and iterations for gradient-based methods to converge to meaningful solutions. Empirically, we observe that for complex-valued data, gradient descent frequently exhibits prolonged plateaus, and advanced optimizers offer limited improvement. In contrast, fixed-pole architectures induce stable and well-conditioned state representations even with limited training data. Numerical results demonstrate that fixed-pole networks achieve superior performance with lower training complexity, making them more suitable for online real-time tasks.
title When Learning Hurts: Fixed-Pole RNN for Real-Time Online Training
topic Machine Learning
url https://arxiv.org/abs/2602.21454