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  4. MAD: A Magnitude And Direction Policy Parametrization for Stability Constrained Reinforcement Learning
 
conference paper

MAD: A Magnitude And Direction Policy Parametrization for Stability Constrained Reinforcement Learning

Furieri, Luca  
•
Shenoy, Sucheth  
•
Saccani, Danilo  
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December 9, 2025
2025 IEEE 64th Conference on Decision and Control (CDC)
2025 IEEE 64th Conference on Decision and Control (CDC)

We introduce magnitude and direction (MAD) policies, a policy parameterization for reinforcement learning (RL) that preserves ℓp closed-loop stability for nonlinear dynamical systems. Despite their completeness in describing all stabilizing controllers, methods based on nonlinear Youla and system-level synthesis are significantly impacted by the difficulty of parametrizing ℓp-stable operators. In contrast, MAD policies introduce explicit feedback on state-dependent features – a key element behind the success of reinforcement learning pipelines – without jeopardizing closed-loop stability. This is achieved by letting the magnitude of the control input be described by a disturbance-feedback ℓp-stable operator, while selecting its direction based on state-dependent features through a universal function approximator. We further characterize the robust stability properties of MAD policies under model mismatch. Unlike existing disturbance-feedback policy parametrizations, MAD policies introduce state-feedback components compatible with model-free RL pipelines, ensuring closed-loop stability with no model information beyond assuming open-loop stability. Numerical experiments show that MAD policies trained with deep deterministic policy gradient (DDPG) methods generalize to unseen scenarios – matching the performance of standard neural network policies while guaranteeing closed-loop stability by design.

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Type
conference paper
DOI
10.1109/cdc57313.2025.11312015
Author(s)
Furieri, Luca  

EPFL

Shenoy, Sucheth  

École Polytechnique Fédérale de Lausanne

Saccani, Danilo  

EPFL

Martin, Andrea  

EPFL

Ferrari Trecate, Giancarlo  

EPFL

Date Issued

2025-12-09

Publisher

IEEE

Published in
2025 IEEE 64th Conference on Decision and Control (CDC)
DOI of the book
10.1109/CDC57313.2025
Start page

942

End page

947

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
SCI-STI-GFT  
Event nameEvent acronymEvent placeEvent date
2025 IEEE 64th Conference on Decision and Control (CDC)

Rio de Janeiro, Brazil

2025-12-09 - 2025-12-12

FunderFunding(s)Grant NumberGrant URL

Swiss National Science Foundation

PZ00P2_208951

Swiss National Science Foundation

51NF40_225155

Swiss National Science Foundation

200021_219431

Available on Infoscience
January 15, 2026
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/258046
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