Causal Matrix Completion: Applications to Offline Causal Reinforcement Learning
summary
Proposes a practical algorithm called synthetic nearest neighbors that combines nearest neighbors and synthetic controls to handle MNAR matrix completion, proves entry-wise consistency and asymptotic normality, and shows it recovers an 80×80 rank‑5 distribution where USVT and SoftImpute break down. Requires a low‑rank latent factor model with selection on latent factors, gives a sample‑efficient experimental design (recover M×N from ~M+N budget; cost ~M K^2+N K^3), and extends to causal tensor completion for offline RL (PER‑SIM learns latent mass and outperforms CADM in MountainCar/HalfCheetah).
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chapters (27)
- 0:00Intro
- 1:21Recommendation systems
- 2:59Contextual bandits
- 4:35Formal setup for matrix completion
- 5:37Models for missingness
- 6:39MCAR & L-MNAR: not a unified approach to sparsity patterns of interest
- 9:07Does the sparsity pattern matter? An empirical example
- 10:35Missing completely at random (MCAR) data
- 12:25"Limited"-missing not at random (L-MNAR) data
- 13:10Missing not at random (MNAR) data
- 15:44Synthetic controls (SC)
- 22:51What type of missing is allowed?-selection on latent factors
- 24:12Other operating assumptions
- 27:16Theoretical results for SNN
- 28:30Simplifying assumption
- 31:33Experiment design: a motivating example from drug design
- 31:56Experiment design: a matrix completion perspective
- 33:18Experiment design: "optimal" observation pattern
- 35:26Towards heteroskedastic variance estimation
- 36:32Heteroskedastic variance estimation algorithm
- 37:19Statistical guarantees
- 38:32An important connection
- 39:23What is behind some of the most popular RL achievements?
- 40:16Simulators are abundant in core engineering systems too
- 41:41PerSim: a motivating example
- 42:18Heterogenous Agents Need Different Policies
- 43:36PerSim: a tensor completion perspective
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