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arXiv · 2610.20014

On the Convergence of Semi-Gradient TD: A Mean Field Perspective

Haruki Settai·Tadashi Kozuno·Shinji Ito
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Abstract

Semi-gradient temporal-difference learning is a core algorithmic component of reinforcement learning, but bootstrapping with function approximation generally induces a non-conservative vector field and can lead to instability. We analyze this effect for two-layer neural networks in the mean-field regime and identify a simple stability mechanism in which entropy-induced relaxation dominates the sensitivity of the moving bootstrap target. Under this condition, we prove exponential convergence to a unique fixed point and quantify its bias relative to the unregularized Bellman solution. We also show that the same mechanism extends to entropy-regularized off-policy control through soft Q-learning.

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Haruki Settai, Tadashi Kozuno, Shinji Ito. 2026-10-14. On the Convergence of Semi-Gradient TD: A Mean Field Perspective. https://arxiv.org/abs/2610.20014

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