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Multi-Hyb: a hybrid algorithm for solving DisCSPs with complex local problems.

Lee, David; Arana, In�s; Ahriz, Hatem; Hui, Kit-Ying


David Lee


Ricardo Baeza-Yates

J�r�me Lang

Sushmita Mitra

Simon Parsons

Gabriella Pasi


A coarse-grained Distributed Constraint Satisfaction Problem (DisCSP) is a constraint problem where several agents, each responsible for solving one part (a complex local problem), cooperate to determine an overall solution. Thus, agents solve the overall problem by finding a solution to their complex local problem which is compatible with the solutions proposed by other agents for their own local problems. Several approaches to solving DisCSPs have been devised and can be classified as systematic search and local search techniques. We present Multi-Hyb, a two-phase hybrid algorithm for solving coarse-grained DisCSPs which uses both systematic and local search during problem solving. Phase 1 generates key partial solutions to the global problem using systematic search. Concurrently, a penalty-based local search algorithm attempts to find a global solution to the problem using these partial solutions. If a global solution is not found in phase 1, the information learnt from phase 1 is used to inform the search carried out during the next phase. Phase two runs a systematic search algorithm on complex variables guided by the following knowledge obtained in phase 1: (i) partial solutions and; (ii) complex local problems which appear more difficult to satisfy. Experimental evaluation demonstrates that Multi-Hyb is competitive in several problem classes in terms of: (i) the communication cost and (ii) the computational effort needed.


LEE, D., ARANA, I., AHRIZ, H. and HUI, K.-Y. 2009. Multi-Hyb: a hybrid algorithm for solving DisCSPs with complex local problems. In Baeza-Yates, R., Lang, J., Mitra, S., Parsons, S. and Pasi, G. (eds.) Proceedings of the 2009 IEEE/WIC/ACM international conference on intelligent agent technology (IAT 2009), co-located with the 2009 IEEE/WIC/ACM international conference on web intelligence (WI 2009), and the joint conference workshops (WI-IAT Workshops 2009), 15-18 September 2009, Milan, Italy. Los Alamitos: IEEE Computer Society [online], volume 2, article number 5284811, pages 379-382. Available from:

Conference Name 2009 IEEE/WIC/ACM international conference on intelligent agent technology (IAT 2009)
Conference Location Milan, Italy
Start Date Sep 15, 2009
End Date Sep 18, 2009
Acceptance Date Sep 30, 2009
Online Publication Date Sep 30, 2009
Publication Date Dec 31, 2009
Deposit Date Jul 6, 2010
Publicly Available Date Jul 6, 2010
Publisher IEEE Computer Society
Volume 2
Article Number 5284811
Pages 379-382
Keywords Agent cooperation; Artificial intelligence; Constraint satisfaction; Distributed constraint satisfaction; Distributed problem solving
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