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Learning Classifier Systems

Learning Classifier Systems. Learning Classifier Systems (LCS). The system has three layers: A performance system that interacts with environment, An apportionment of credit algorithm that rates rules as to usefulness,

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Learning Classifier Systems

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  1. Learning Classifier Systems

  2. Learning Classifier Systems (LCS) • The system has three layers: • A performance system that interacts with environment, • An apportionment of credit algorithm that rates rules as to usefulness, • A rule discovery algorithm that generates plausible new rules to replace less useful rules.

  3. Performance System Cycles • Message is posted in the message list from the input interface. • Each rule is matched against the message list • All matching rules compete to post in the next message list via bidding process; winning rule posts in the new message list • The output interface checks the new message and produces an effector action. • The new message list replaces the previous one. • Repeat.

  4. Overview of LCS

  5. Rule format • Rule • Condition = {0,1,#}k • Action = message to be posted in the message list • Strength = rule’s usefulness to the system

  6. kind ears num. of legs smart scream runaway kiss Example (Wolf or Grandmother?) Encoding teeth Wolf 1 0 1 1 1 # 1 1 0 GrandMa 0 1 0 0 1 # 0 0 1

  7. Matching [N] [M]

  8. Bidding Process • Bid(R,t) = β × specificity(R) × Strength(R,t) • Specificity(R)= number of non # / k [M] β = 0.2 Bid(r1) = 0.2 × ¼ × 100 = 5 Bid(r3) = 0.2 × ½ × 100 = 10 r3 posts its message in the new message list.

  9. Credit assignment: Bucket Brigade Bucket 10 r3 coupled Bucket r5 150 executed Reward Environment 200

  10. Credit assignment: Bucket Brigade Bucket 10 r3 Bucket r5 150 Reward Environment 200

  11. Genetic Algorithms • Fitness = rule strength • Parents: Strong classifiers (best, roulette wheel, etc.) • Mutation: alter parts of parent’s string • Crossover: exchange parts of parents’ strings • Offspring replaces a weak rule.

  12. Genetic Algorithms (cont.) Crossover Crossover point Parent 1 Parent 2 Mutation Parent 1 Parent 2

  13. Maze Environment (Signal smell-ahead bump heading score location) Environment

  14. References • A Mathematical framework for Studying Learning in Classifier Systems, John H. Holland, Phsyca D, Vol 2, No 1-3, 1986, pp. 307-317 • A First Order Logic Classifier System, Drew Mellor Gecco ’05

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