Package org.jacop.constraints

Class ValuePrecede

  • All Implemented Interfaces:
    SatisfiedPresent, Stateful, UsesQueueVariable
    public class ValuePrecede
extends Constraint
implements UsesQueueVariable, Stateful, SatisfiedPresent
    It defines Value Precedence constraint for integers.

    Value precedence of s over t in an integer sequence x = [x0,..., xn−1] means if there exists j such that xj = t, then there must exist i < j such that xi = s.

    The algorithm is based on paper "Global Constraints for Integer and Set Value Precedence" by Y. C. Law, J. H. Lee Principles and Practice of Constraint Programming (CP'2004).

    Version:
    4.8

    • Field Detail

      • idNumber

        static final java.util.concurrent.atomic.AtomicInteger idNumber

      • x

        public final IntVar[] x
        It specifies lists of variables for the constraint.

      • n

        private int n

      • s

        protected final int s
        It specifies values s and t for the constraint.

      • t

        protected final int t
        It specifies values s and t for the constraint.

      • alpha

        private TimeStamp<java.lang.Integer> alpha
        Defines variables alpha, beta, gamma for the algorithm

      • beta

        private TimeStamp<java.lang.Integer> beta

      • gamma

        private TimeStamp<java.lang.Integer> gamma

      • firstConsistencyCheck

        private boolean firstConsistencyCheck

      • varQueue

        private java.util.LinkedHashSet<IntVar> varQueue

      • varMap

        private final java.util.Map<IntVar,​java.lang.Integer> varMap

    • Constructor Detail

      • ValuePrecede

        public ValuePrecede​(int s,
                    int t,
                    IntVar[] x)
        It constructs ValuePrecede.
        Parameters:
        s - value occuring first
        t - value occuring next
        x - list of arguments x's.

      • ValuePrecede

        public ValuePrecede​(int s,
                    int t,
                    java.util.List<IntVar> x)
        It constructs ValuePrecede.
        Parameters:
        s - value occuring first
        t - value occuring next
        x - list of arguments x's.

    • Method Detail

      • 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.

      • 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.

      • initialize

        private void initialize()

      • propagate

        private void propagate​(int i)

      • updateBeta

        private void updateBeta()

      • checkGamma

        private void checkGamma​(int i)

      • satisfied

        public boolean satisfied()
        Description copied from interface: SatisfiedPresent
        It checks if the constraint is satisfied. It can return false even if constraint is satisfied but not all variables in its scope are grounded. It needs to return true if all variables in its scope are grounded and constraint is satisfied.

        Implementations of this interface for constraints that are not PrimitiveConstraint may require constraint imposition and consistency check as a requirement to work correctly.

        Specified by:
        satisfied in interface SatisfiedPresent
        Returns:
        true if constraint is possible to verify that it is satisfied.

      • queueVariable

        public void queueVariable​(int level,
                          Var var)
        Description copied from class: Constraint
        This is a function called to indicate which variable in a scope of constraint has changed. It also indicates a store level at which the change has occurred.
        Overrides:
        queueVariable in class Constraint
        Parameters:
        level - the level of the store at which the change has occurred.
        var - variable which has changed.

      • removeLevel

        public void removeLevel​(int level)
        Description copied from interface: Stateful
        This function is called in case of the backtrack, so a constraint can clear the queue of changed variables which is no longer valid. This function is called *before* all timestamps, variables, mutablevariables have reverted to their previous value.
        Specified by:
        removeLevel in interface Stateful
        Parameters:
        level - the level which is being removed.

      • 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