Andrea Vasco Grieco
On the Role of Policy Variance in Proximal Policy Optimization for Continuous-Action Robot Control.
Rel. Raffaello Camoriano, Daniele Pucci, Evelyn D'Elia, Edoardo Caldarelli, Lorenzo Rosasco. Politecnico di Torino, Master of science program in Data Science And Engineering, 2026
Abstract
This thesis explores the geometric properties of the reinforcement learning algorithm Proximal Policy Optimization (PPO) in the context of continuous action spaces and isotropic deep Gaussian policies, with standard deviation σ. Despite the popularity of PPO in this setting, few works examine theoretical and geometric implications of the algorithm structure. However, these can prove fundamental to improve the existing heuristics and to develop better strategies. Our focus is on the characterization of the role of σ, which is often assumed to only affect exploration. However, we show that it adds relevant geometric implications. Firstly, we develop novel bounds for the gradient norm and eigenvalues of the loss characterizing its optimization landscape.
These show that the annealing of σ, which happens during optimization, causes ill-conditioning and makes the problem difficult to optimize
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