What is reinforcement learning?

Reinforcement learning (RL) is a machine learning approach where an agent learns to make decisions by interacting with an environment to maximize cumulative rewards. Unlike supervised learning, which relies on labeled data, RL uses trial and error: the agent takes actions, observes outcomes, and adjusts its strategy based on feedback in the form of rewards or penalties. The goal is to learn a policy—a set of rules—that maps states of the environment to actions that yield the highest long-term rewards. Key components include the agent (the decision-maker), the environment (the world the agent operates in), actions (choices the agent makes), states (the environment’s current condition), and rewards (feedback signals).

In RL, the learning process involves balancing exploration (trying new actions to discover their effects) and exploitation (using known actions that yield high rewards). For example, consider training an AI to play a video game. The agent might initially move randomly (exploration), but as it learns which actions increase the game score (reward), it prioritizes those actions (exploitation). Algorithms like Q-learning and Deep Q-Networks (DQN) use value functions to estimate the expected reward of actions in specific states. Policy gradient methods directly optimize the agent’s behavior by adjusting probabilities of taking certain actions. These approaches often rely on iterative updates, where the agent refines its strategy over time through repeated interactions with the environment.

Practical applications of RL span diverse domains. In robotics, RL trains robots to perform tasks like walking or grasping objects by rewarding successful movements. In recommendation systems, RL optimizes content suggestions by rewarding user engagement (e.g., clicks or watch time). Game AI, such as AlphaGo, uses RL to master complex strategies through self-play. However, RL faces challenges like sparse rewards (e.g., winning a game after many steps) and high computational costs. Developers often use frameworks like OpenAI Gym or libraries like TensorFlow Agents to simulate environments and test algorithms. Understanding RL requires familiarity with concepts like Markov Decision Processes (MDPs), which model decision-making under uncertainty, and trade-offs between immediate and future rewards (discount factors).