arXiv Machine Learning By Lars van der Laan, Nathan Kallus

Fitted Occupancy-Ratio Evaluation without Bellman Completeness

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arXiv:2607. 05375v1 Announce Type: cross Abstract: Occupancy ratios correct distribution shift in offline reinforcement learning and are central to off-policy evaluation.

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arXiv Machine Learning
Sep 1

Fitted Q-Evaluation without Bellman Completeness via Occupancy Weighting

The paper introduces occupancy-weighted Fitted Q-Evaluation (FQE), a regression-based off‑policy evaluation method that replaces the standard offline distribution weights with a target‑policy discounted occupancy ratio. This weighting aligns the projection norm with the target policy’s dynamics, restoring contraction of the Bellman operator and eliminating the need for Bellman completeness. The authors provide finite‑sample guarantees that separate iteration, statistical, approximation, and ratio‑estimation errors, and show that exact occupancy weighting combined with fitted occupancy‑ratio evaluation yields consistent estimation under coverage without requiring critic‑side completeness.

By Lars van der Laan, Nathan Kallus