通过可视化批评者损失景观,解析在线强化学习的优化行为。
Visualizing Critic Match Loss Landscapes for Interpretation of Online Reinforcement Learning Control Algorithms
- 将批评者参数轨迹投影到低维子空间,构建损失景观图
- 揭示稳定收敛与不稳定学习对应的景观特征差异
- 适合研究强化学习机制或调试控制算法的学者
强化学习在多种场景中表现强劲,但在系统动态变化时性能难以保证,常依赖用户经验。针对具有演员-批评者结构的算法,批评者神经网络反映了强化学习中的近似与优化过程。为系统解读动态控制问题中的算法机制,本文提出一种在线强化学习的批评者匹配损失景观可视化方法。该方法通过将记录的批评者参数轨迹投影到低维线性子空间,利用固定参考状态样本和时序差分目标,在投影参数网格上评估批评者匹配损失,生成三维损失曲面与二维优化路径,刻画批评者学习行为。为进一步支持量化分析,引入定量景观指标与归一化系统性能指数,实现不同训练结果间的结构化比较。实验基于行动相关启发式动态规划算法,在倒立摆与航天器姿态控制任务中验证。对比不同投影方法与训练阶段的分析显示,稳定收敛与不稳定学习对应不同的景观特性。该框架实现了在线强化学习中批评者优化行为的定性与定量解释。
原文摘要 · Abstract (English)
Reinforcement learning has proven its power on various occasions. However, its performance is not always guaranteed when system dynamics change. Instead, it largely relies on users' empirical experience. For reinforcement learning algorithms with an actor-critic structure, the critic neural network reflects the approximation and optimization process in the RL algorithm. Analyzing the performance of the critic neural network helps to understand the mechanism of the algorithm. To support systematic interpretation of such algorithms in dynamic control problems, this work proposes a critic match loss landscape visualization method for online reinforcement learning. The method constructs a loss landscape by projecting recorded critic parameter trajectories onto a low-dimensional linear subspace. The critic match loss is evaluated over the projected parameter grid using fixed reference state samples and temporal-difference targets. This yields a three-dimensional loss surface together with a two-dimensional optimization path that characterizes critic learning behavior. To extend analysis beyond visual inspection, quantitative landscape indices and a normalized system performance index are introduced, enabling structured comparison across different training outcomes. The approach is demonstrated using the Action-Dependent Heuristic Dynamic Programming algorithm on cart-pole and spacecraft attitude control tasks. Comparative analyses across projection methods and training stages reveal distinct landscape characteristics associated with stable convergence and unstable learning. The proposed framework enables both qualitative and quantitative interpretation of critic optimization behavior in online reinforcement learning.
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