TY - GEN
T1 - A soft constraint of equality
T2 - 14th International Conference on Principles and Practice of Constraint Programming, CP 2008
AU - Hebrard, Emmanuel
AU - O'Sullivan, Barry
AU - Razgon, Igor
PY - 2008/11/26
Y1 - 2008/11/26
N2 - We introduce the SoftAllEqual global constraint, which maximizes the number of equalities holding between pairs of assignments to a set of variables. We study the computational complexity of propagating this constraint, showing that it is intractable in general, since maximizing the number of pairs of equally assigned variables in a set is NP-hard. We propose three ways of coping with NP-hardness. Firstly, we develop a greedy linear-time algorithm to approximate the maximum number of equalities within a factor of 2. Secondly, we identify a tractable (polynomial) class for this constraint. Thirdly, we identify a parameter based on this class and show that the SoftAllEqual constraint is fixed-parameter tractable with respect to this parameter.
AB - We introduce the SoftAllEqual global constraint, which maximizes the number of equalities holding between pairs of assignments to a set of variables. We study the computational complexity of propagating this constraint, showing that it is intractable in general, since maximizing the number of pairs of equally assigned variables in a set is NP-hard. We propose three ways of coping with NP-hardness. Firstly, we develop a greedy linear-time algorithm to approximate the maximum number of equalities within a factor of 2. Secondly, we identify a tractable (polynomial) class for this constraint. Thirdly, we identify a parameter based on this class and show that the SoftAllEqual constraint is fixed-parameter tractable with respect to this parameter.
UR - http://www.scopus.com/inward/record.url?scp=56449090180&partnerID=8YFLogxK
U2 - 10.1007/978-3-540-85958-1_24
DO - 10.1007/978-3-540-85958-1_24
M3 - Conference contribution
AN - SCOPUS:56449090180
SN - 3540859578
SN - 9783540859574
T3 - Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
SP - 358
EP - 371
BT - Principles and Practice of Constraint Programming - 14th International Conference, CP 2008, Proceedings
Y2 - 14 September 2008 through 18 September 2008
ER -