org.jacop.constraints

Class NoGood

java.lang.Object

org.jacop.constraints.DecomposedConstraint

org.jacop.constraints.Constraint

org.jacop.constraints.PrimitiveConstraint

org.jacop.constraints.NoGood

public class NoGood
extends PrimitiveConstraint

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:

4.2

Author:

Radoslaw Szymanek and Krzysztof Kuchcinski

Field Summary

Fields

Modifier and Type	Field and Description
int[]	listOfValues It specifies a list of values in no-good constraint.
IntVar[]	listOfVars It specifies a list of variables in no-good constraint.
static String[]	xmlAttributes It specifies the arguments required to be saved by an XML format as well as the constructor being called to recreate an object from an XML format.

Fields inherited from class org.jacop.constraints.PrimitiveConstraint

notConsistencyPruningEvents

Fields inherited from class org.jacop.constraints.Constraint

atomicExecution, consistencyPruningEvents, earlyTerminationOK, id, increaseWeight, numberArgs, numberId, trace

Fields inherited from class org.jacop.constraints.DecomposedConstraint

queueIndex

Constructor Summary

Constructors

Constructor and Description
NoGood(ArrayList<? extends IntVar> listOfVars, ArrayList<Integer> listOfValues) It creates a no-good constraint.
NoGood(IntVar[] listOfVars, int[] listOfValues) It creates a no-good constraint.

Method Summary

Modifier and Type	Method and Description
ArrayList<Var>	arguments() It returns the variables in a scope of the constraint.
void	consistency(Store store) It is a (most probably incomplete) consistency function which removes the values from variables domains.
int	getConsistencyPruningEvent(Var var) It retrieves the pruning event which causes reevaluation of the constraint.
int	getNestedPruningEvent(Var var, boolean mode) It retrieves the pruning event for which any composed constraint which uses this constraint should be evaluated.
int	getNotConsistencyPruningEvent(Var var) It retrieves the pruning event which causes reevaluation of the constraint notConsistency() function.
void	impose(Store store) It imposes the constraint in a given store.
void	increaseWeight() It increases the weight of the variables in the constraint scope.
void	notConsistency(Store store) It makes pruning in such a way that constraint is notConsistent.
boolean	notSatisfied() It checks if constraint would be always not satisfied.
void	removeConstraint() This function does nothing as constraints can not be removed for a given level.
boolean	satisfied() First time consistency function does pruning is the last time it will be called.
String	toString() It produces a string representation of a constraint state.

Methods inherited from class org.jacop.constraints.PrimitiveConstraint

include, setNotConsistencyPruningEvent

Methods inherited from class org.jacop.constraints.Constraint

cleanAfterFailure, decompose, getGuideConstraint, getGuideValue, getGuideVariable, id, impose, imposeDecomposition, numberArgs, queueVariable, removeLevel, removeLevelLate, requiresMonotonicity, setConsistencyPruningEvent, supplyGuideFeedback

Methods inherited from class org.jacop.constraints.DecomposedConstraint

auxiliaryVariables, derivative, imposeDecomposition

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

listOfVars

public IntVar[] listOfVars

It specifies a list of variables in no-good constraint.

listOfValues

public int[] listOfValues

It specifies a list of values in no-good constraint.

xmlAttributes

public static String[] xmlAttributes

It specifies the arguments required to be saved by an XML format as well as the constructor being called to recreate an object from an XML format.

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(ArrayList<? extends IntVar> listOfVars,
              ArrayList<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

arguments

public ArrayList<Var> arguments()

Description copied from class: Constraint

It returns the variables in a scope of the constraint.

Specified by:

arguments in class Constraint

Returns:

variables in a scope of the constraint.

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.

getConsistencyPruningEvent

public int getConsistencyPruningEvent(Var var)

Description copied from class: Constraint

It retrieves the pruning event which causes reevaluation of the constraint.

Specified by:

getConsistencyPruningEvent in class Constraint

Parameters:

var - variable for which pruning event is retrieved

Returns:

it returns the int code of the pruning event (GROUND, BOUND, ANY, NONE)

impose

public void impose(Store store)

Description copied from class: Constraint

It imposes the constraint in a given store.

Specified by:

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.

Specified by:

removeConstraint in class Constraint

satisfied

public boolean satisfied()

First time consistency function does pruning is the last time it will be called. In addition, nogood constraints are not attached in a normal way to variable. Therefore this function will not be called. It returns false by default.

Specified by:

satisfied in class Constraint

Returns:

true if the constraint is for certain satisfied, false otherwise.

toString

public String toString()

Description copied from class: Constraint

It produces a string representation of a constraint state.

Specified by:

toString in class Constraint

increaseWeight

public void increaseWeight()

Description copied from class: Constraint

It increases the weight of the variables in the constraint scope.

Specified by:

increaseWeight in class Constraint

notSatisfied

public boolean notSatisfied()

Description copied from class: PrimitiveConstraint

It checks if constraint would be always not satisfied.

Specified by:

notSatisfied in class PrimitiveConstraint

Returns:

true if constraint must be notSatisfied, false otherwise.

getNestedPruningEvent

public int getNestedPruningEvent(Var var,
                                 boolean mode)

Description copied from class: PrimitiveConstraint

It retrieves the pruning event for which any composed constraint which uses this constraint should be evaluated. This events are the ones which can change satisfied status?

Specified by:

getNestedPruningEvent in class PrimitiveConstraint

Parameters:

var - for which pruning event is retrieved

mode - decides if pruning event for consistency or nonconsistency is required.

Returns:

pruning event associated with the given variable for a given consistency mode.

getNotConsistencyPruningEvent

public int getNotConsistencyPruningEvent(Var var)

Description copied from class: PrimitiveConstraint

It retrieves the pruning event which causes reevaluation of the constraint notConsistency() function.

Specified by:

getNotConsistencyPruningEvent in class PrimitiveConstraint

Parameters:

var - for which pruning event is retrieved

Returns:

the int denoting the pruning event associated with given variable.

notConsistency

public void notConsistency(Store store)

Description copied from class: PrimitiveConstraint

It makes pruning in such a way that constraint is notConsistent. It removes values which always belong to a solution.

Specified by:

notConsistency in class PrimitiveConstraint

Parameters:

store - the constraint store in which context the notConsistency technique is evaluated.