Bridging Continuous-time LQR and Reinforcement Learning via Gradient Flow of the Bellman Error

Fuente: arXiv
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Autores principales: Gießler, Armin, Malan, Albertus Johannes, Hohmann, Sören
Formato: Preprint
Publicado: 2025
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author Gießler, Armin
Malan, Albertus Johannes
Hohmann, Sören
author_facet Gießler, Armin
Malan, Albertus Johannes
Hohmann, Sören
contents In this paper, we present a novel method for computing the optimal feedback gain of the infinite-horizon Linear Quadratic Regulator (LQR) problem via an ordinary differential equation. We introduce a novel continuous-time Bellman error, derived from the Hamilton-Jacobi-Bellman (HJB) equation, which quantifies the suboptimality of stabilizing policies and is parametrized in terms of the feedback gain. We analyze its properties, including its effective domain, smoothness, coerciveness and show the existence of a unique stationary point within the stability region. Furthermore, we derive a closed-form gradient expression of the Bellman error that induces a gradient flow. This converges to the optimal feedback and generates a unique trajectory which exclusively comprises stabilizing feedback policies. Additionally, this work advances interesting connections between LQR theory and Reinforcement Learning (RL) by redefining suboptimality of the Algebraic Riccati Equation (ARE) as a Bellman error, adapting a state-independent formulation, and leveraging Lyapunov equations to overcome the infinite-horizon challenge. We validate our method in a simulation and compare it to the state of the art.
format Preprint
id arxiv_https___arxiv_org_abs_2506_09685
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Bridging Continuous-time LQR and Reinforcement Learning via Gradient Flow of the Bellman Error
Gießler, Armin
Malan, Albertus Johannes
Hohmann, Sören
Systems and Control
In this paper, we present a novel method for computing the optimal feedback gain of the infinite-horizon Linear Quadratic Regulator (LQR) problem via an ordinary differential equation. We introduce a novel continuous-time Bellman error, derived from the Hamilton-Jacobi-Bellman (HJB) equation, which quantifies the suboptimality of stabilizing policies and is parametrized in terms of the feedback gain. We analyze its properties, including its effective domain, smoothness, coerciveness and show the existence of a unique stationary point within the stability region. Furthermore, we derive a closed-form gradient expression of the Bellman error that induces a gradient flow. This converges to the optimal feedback and generates a unique trajectory which exclusively comprises stabilizing feedback policies. Additionally, this work advances interesting connections between LQR theory and Reinforcement Learning (RL) by redefining suboptimality of the Algebraic Riccati Equation (ARE) as a Bellman error, adapting a state-independent formulation, and leveraging Lyapunov equations to overcome the infinite-horizon challenge. We validate our method in a simulation and compare it to the state of the art.
title Bridging Continuous-time LQR and Reinforcement Learning via Gradient Flow of the Bellman Error
topic Systems and Control
url https://arxiv.org/abs/2506.09685