A Hyper-arc Consistency Algorithm for the Soft Alldifferent Constraint
نویسنده
چکیده
This paper presents an algorithm that achieves hyper-arc consistency for the soft alldifferent constraint. To this end, we prove and exploit the equivalence with a minimum-cost flow problem. Consistency of the constraint can be checked in O(nm) time, and hyper-arc consistency is achieved in O(m) time, where n is the number of variables involved and m is the sum of the cardinalities of the domains. It improves a previous method that did not ensure hyper-arc consistency.
منابع مشابه
Generalised arc consistency for the AllDifferent constraint: An empirical survey
The AllDifferent constraint is a crucial component of any constraint toolkit, language or solver, since it is very widely used in a variety of constraint models. The literature contains many different versions of this constraint, which trade strength of inference against computational cost. In this paper, we focus on the highest strength of inference, enforcing a property known as generalised a...
متن کاملThe Alldifferent Constraint: Exploiting Strongly-connected Components and Other Efficiency Measures
The AllDifferent constraint is a crucial component of any constraint toolkit, language or solver, since it is very widely used in a variety of constraint models. The literature contains many different versions of this constraint, which trade strength of inference against computational cost. In this paper, we focus on the highest strength of inference (enforcing a property known as generalised a...
متن کاملGeneralizing AllDifferent: The SomeDifferent Constraint
We introduce the SomeDifferent constraint as a generalization of AllDifferent. SomeDifferent requires that values assigned to some pairs of variables will be different. It has many practical applications. For example, in workforce management, it may enforce the requirement that the same worker is not assigned to two jobs which are overlapping in time. Propagation of the constraint for hyper-arc...
متن کاملA Probabilistic Study of Bound Consistency for the Alldifferent Constraint
This paper introduces a mathematical model for bound consistency of the constraint AllDifferent. It allows us to compute the probability that the filtering algorithm effectively removes at least one value in the variable domains. A complete study of the bound consistency properties is then proposed. It identifies several behaviors depending on some macroscopic quantities related to the variable...
متن کاملThe 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...
متن کامل