What is a classifier system?: a gentle introduction to accuracy-based classifier systems such as XCS

A learning classifier system (LCS) is an adaptive system that learns to perform the best action given its input. By “best” is generally meant the action that will receive the most reward or reinforcement from the system’s environment. By “input” is meant the environment as sensed by the system, usually a vector of numerical values. The set of available actions depends on the system context: if the system is a mobile robot, the available actions may be physical: “turn left”, “turn right”, etc. In a classification context, the available actions may be “yes”, “no”, or “benign”, “malignant”, etc. In a decision context, for instance a financial one, the actions might be “buy”, “sell”, etc. In general, an LCS is a simple model of an intelligent agent interacting with an environment.