The AllDifferent Constraint with Precedences

We propose ALLDIFFPREC, a new global constraint that combines together an ALLDIFFERENT constraint with precedence constraints that strictly order given pairs of variables. We identify a number of applications for this global constraint including instruction scheduling and symmetry breaking. We give an efficient propagation algorithm that enforces bounds consistency on this global constraint. We show how to implement this propagator using a decomposition that extends the bounds consistency enforcing decomposition proposed for the ALLDIFFERENT constraint. Finally, we prove that enforcing domain consistency on this global constraint is NP-hard in general.

• Type: Journal
• Year: 2011
• Where: CORR
• Authors: Christian Bessiere, Nina Narodytska, Claude-Guy Quimper, Toby Walsh
• Keywords: Consistency, CORR 2011, Education, Efficient Propagation Algorithm, Global Constraint