Learning classifier system

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A learning classifier system, or LCS, is a machine learning system with close links to reinforcement learning and genetic algorithms. First described by John Holland, his LCS consisted of a population of binary rules on which a genetic algorithm altered and selected the best rules. Rule fitness was based on a reinforcement learning technique.


Learning classifier systems can be split into two types depending upon where the genetic algorithm acts. A Pittsburgh-type LCS has a population of separate rule sets, where the genetic algorithm recombines and reproduces the best of these rule sets. In a Michigan-style LCS there is only a single set of rules in a population and the algorithm's action focuses on selecting the best classifiers within that set. Michigan-style LCSs have two main types of fitness definitions: strength-based (e.g. ZCS) and accuracy-based (e.g. XCS). The term "learning classifier system" most often refers to Michigan-style LCSs.

Initially the classifiers or rules were binary, but recent research has expanded this representation to include real-valued, neural network, and functional (S-expression) conditions.[citation needed]

Learning classifier systems are not fully understood remains an area of active research.[citation needed] Despite this, they have been successfully applied in many problem domains.


  • Urbanowicz, Ryan J.; Moore, Jason H. (January 2009), "Learning Classifier Systems: A Complete Introduction, Review, and Roadmap", J. Artif. Evol. App., New York, NY, United States: Hindawi Publishing Corp., 2009: 1:1–1:25, doi:10.1155/2009/736398 .

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