IPSThe inverse propensity score (IPS) estimator, which is used for off-policy evaluation in a contextual bandit problem, is well explained here: Doubly Robust Policy Evaluation andOptimizationin the paper https://arxiv.org/pdf/1503.02834.pdfDoubly Robust Policy Evaluation and Optimization.
The old policy $\mu$, or the behavior policy, is okay to be non-stationary in the IPS estimator even if the new policy $\nu$, or the target policy, should be stationary.
I wonder if that isIs this true for ISthe importance sampling (IS) estimator, which seems to be a variant of IPS, for off-policy evaluation in a reinforcement learning problem. IS?
IS estimator is explained here: Doubly Robust Off-policy Value Evaluation for Reinforcement Learningin this paper https://arxiv.org/abs/1511.03722Doubly Robust Off-policy Value Evaluation for Reinforcement Learning. The
The target policy should be stationary, but can the old policy be non-stationary in the IS estimator?