Package org.jacop.constraints

Class NoGood

  • public class NoGood
extends Constraint
    NoGood constraints implements a constraint which disallows given combination of values for given variables. NoGoods are special constraints as they can be only triggered only when all variables except one are grounded and equal to disallow values. This allows efficient implementation based on watched literals idea from SAT community.

    Do not be fooled by watched literals, if you add thousands of no-goods then traversing even 1/10 of them if they are watched by variable which has been grounded can slow down search considerably.

    NoGoods constraints are imposed at all levels once added. Do not use in subsearches, as it will not take into account the assignments performed in master search.

    Version:
    4.8

    • Field Detail

      • idNumber

        static java.util.concurrent.atomic.AtomicInteger idNumber

      • listOfVars

        protected IntVar[] listOfVars
        It specifies a list of variables in no-good constraint.

      • listOfValues

        protected int[] listOfValues
        It specifies a list of values in no-good constraint.

      • firstWatch

        private IntVar firstWatch

      • firstValue

        private int firstValue

      • secondWatch

        private IntVar secondWatch

      • secondValue

        private int secondValue

    • Constructor Detail

      • NoGood

        public NoGood​(IntVar[] listOfVars,
              int[] listOfValues)
        It creates a no-good constraint.
        Parameters:
        listOfVars - the scope of the constraint.
        listOfValues - no-good values which all-together assignment to variables within constraint scope is a no-good.

      • NoGood

        public NoGood​(java.util.List<? extends IntVar> listOfVars,
              java.util.List<java.lang.Integer> listOfValues)
        It creates a no-good constraint.
        Parameters:
        listOfVars - the scope of the constraint.
        listOfValues - no-good values which all-together assignment to variables within constraint scope is a no-good.

    • Method Detail

      • commonInitialization

        private void commonInitialization​(IntVar[] listOfVars,
                                  int[] listOfValues)

      • consistency

        public void consistency​(Store store)
        Description copied from class: Constraint
        It is a (most probably incomplete) consistency function which removes the values from variables domains. Only values which do not have any support in a solution space are removed.
        Specified by:
        consistency in class Constraint
        Parameters:
        store - constraint store within which the constraint consistency is being checked.

      • impose

        public void impose​(Store store)
        Description copied from class: Constraint
        It imposes the constraint in a given store.
        Overrides:
        impose in class Constraint
        Parameters:
        store - the constraint store to which the constraint is imposed to.

      • removeConstraint

        public void removeConstraint()
        This function does nothing as constraints can not be removed for a given level. In addition, watched literals mechanism makes sure that constraint is not put in the queue when it can not propagate.
        Overrides:
        removeConstraint in class Constraint

      • toString

        public java.lang.String toString()
        Description copied from class: Constraint
        It produces a string representation of a constraint state.
        Overrides:
        toString in class Constraint