Reinforcement Learning
Reinforcement learning is learning from consequences over time. The object being learned is not a label predictor but a policy or value estimate for sequential decisions under uncertainty.
Mental model
An agent observes a state, chooses an action, receives a reward, and transitions. Return aggregates future rewards; a policy maps states to action distributions; value functions summarize expected return. Bellman equations expose the recursive structure that most RL algorithms approximate.
Current overview
Candidate note roadmap
mdps-returns-policies-and-values— formal problem definition and assumptions.bellman-equations-and-dynamic-programming— policy evaluation, improvement, and value iteration.monte-carlo-and-temporal-difference-learning— sampled returns, bootstrapping, bias, and variance.q-learning-and-deep-q-networks— off-policy control, replay, target networks, and instability.policy-gradients-from-first-principles— score-function estimator, baselines, and variance reduction.actor-critic-methods— learned critics, advantage estimation, and implementation tradeoffs.exploration-and-credit-assignment— uncertainty, sparse rewards, and long horizons.offline-rl-and-dataset-coverage— distribution shift, conservatism, and evaluation without deployment.model-based-rl-and-world-models— learned dynamics, planning, model error, and compounding bias.reward-hacking-rlhf-and-rlaif— specification gaming and connections to model alignment.
Scope
This branch separates RL as a field from RLHF as one adaptation technique. Examples start in tabular environments before neural approximators hide the mechanism.
Connects to: Classical AI and Reasoning · RLHF with PPO · Autonomy and Control
Core sources
- Reinforcement Learning: An Introduction — canonical free text by Sutton and Barto.
- David Silver's Reinforcement Learning course — rigorous lectures from MDPs through policy gradients.
- OpenAI Spinning Up — equations and minimal implementations for deep RL.
- Offline Reinforcement Learning: Tutorial, Review, and Perspectives — map of the offline setting and its distribution-shift problem.