Chapter

Abstraction, Reformulation and Approximation

Volume 3607 of the series Lecture Notes in Computer Science pp 121-133

Hierarchical Heuristic Search Revisited

  • Robert C. HolteAffiliated withComputing Science Department, University of Alberta
  • , Jeffery GrajkowskiAffiliated withComputing Science Department, University of Alberta
  • , Brian TannerAffiliated withComputing Science Department, University of Alberta

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Abstract

Pattern databases enable difficult search problems to be solved very quickly, but are large and time-consuming to build. They are therefore best suited to situations where many problem instances are to be solved, and less than ideal when only a few instances are to be solved. This paper examines a technique – hierarchical heuristic search - especially designed for the latter situation. The key idea is to compute, on demand, only those pattern database entries needed to solve a given problem instance. Our experiments show that Hierarchical IDA* can solve individual problems very quickly, up to two orders of magnitude faster than the time required to build an entire high-performance pattern database.