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Snake Lex: An Alternative to Double Lex
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Snake Lex: An Alternative to Double Lex
Andrew Grayland17 , Ian Miguel17 and Colva M. Roney-Dougal18 
| (17) |
School of Comp. Sci., St Andrews, UK |
| (18) |
School of Maths and Stats, St Andrews, UK |
Abstract
Complete row and column symmetry breaking in constraint models using the lex leader method is generally prohibitively costly.
Double lex, which is derived from lex leader, is commonly used in practice as an incomplete symmetry-breaking method for row
and column symmetries. Double lex is based on a row-wise canonical variable ordering. However, this choice is arbitrary. We investigate other canonical orderings and focus on one
in particular: snake ordering. From this we derive a corresponding incomplete set of symmetry breaking constraints, snake lex. Experimental data comparing double lex and snake lex shows that snake lex is substantially better than double lex in many
cases.
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