org.jacop.constraints

Class LexOrder

java.lang.Object

org.jacop.constraints.DecomposedConstraint<Constraint>

org.jacop.constraints.Constraint

org.jacop.constraints.LexOrder

All Implemented Interfaces:

RemoveLevelLate, SatisfiedPresent, Stateful, UsesQueueVariable

public class LexOrder
extends Constraint
implements UsesQueueVariable, Stateful, SatisfiedPresent, RemoveLevelLate

It constructs a LexOrder (lexicographical order) constraint.

The algorithm is based on paper

"Propagation algorithms for lexicographic ordering constraints" by Alan M. Frisch, Brahim Hnich, Zeynep Kiziltan, Ian Miguel, and Toby Walsh , Artificial Intelligence 170 (2006) 803-834.

Version:

4.9

Author:

Krzysztof Kuchcinski and Radoslaw Szymanek

Field Summary

Fields

Modifier and Type	Field and Description
boolean	lexLT Lex enforcing "<" relationship (true).
boolean	originalLexLT
IntVar[]	x Two vectors that have to be lexicographically ordered.
IntVar[]	y

Fields inherited from class org.jacop.constraints.Constraint

atomicExecution, consistencyPruningEvents, constraintScope, earlyTerminationOK, increaseWeight, numberId, scope, trace

Fields inherited from class org.jacop.constraints.DecomposedConstraint

queueIndex

Constructor Summary

Constructors

Constructor and Description
LexOrder(IntVar[] x, IntVar[] y) It creates a lexicographical order for vectors x and y,
LexOrder(IntVar[] x, IntVar[] y, boolean lt)

Method Summary

Modifier and Type	Method and Description
void	consistency(Store store) It is a (most probably incomplete) consistency function which removes the values from variables domains.
protected void	establishGACInit()
int	getDefaultConsistencyPruningEvent()
void	impose(Store store) It imposes the constraint in a given store.
void	queueVariable(int level, Var var) This is a function called to indicate which variable in a scope of constraint has changed.
void	removeLevel(int level) This function is called in case of the backtrack, so a constraint can clear the queue of changed variables which is no longer valid.
void	removeLevelLate(int level) This function is called in case of the backtrack.
boolean	satisfied() It checks if the constraint is satisfied.
String	toString() It produces a string representation of a constraint state.
void	updateAlpha()
void	updateBeta(int i)

Methods inherited from class org.jacop.constraints.Constraint

afc, arguments, cleanAfterFailure, decompose, getConsistencyPruningEvent, getGuideConstraint, getGuideValue, getGuideVariable, grounded, grounded, id, impose, imposeDecomposition, increaseWeight, intArrayToString, long2int, numberArgs, removeConstraint, requiresMonotonicity, setConsistencyPruningEvent, setConstraintScope, setScope, setScope, setScope, setScope, setScope, setWatchedVariableGrounded, supplyGuideFeedback, updateAFC, watchedVariableGrounded

Methods inherited from class org.jacop.constraints.DecomposedConstraint

auxiliaryVariables, checkInput, checkInput, checkInputForDuplication, checkInputForDuplicationSkipSingletons, checkInputForNullness, checkInputForNullness, checkInputForNullness, derivative, getDubletonsSkipSingletons, imposeDecomposition

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.jacop.api.Stateful

isStateful

Field Detail

x

public IntVar[] x

Two vectors that have to be lexicographically ordered.

y

public IntVar[] y

lexLT

public boolean lexLT

Lex enforcing "<" relationship (true).

originalLexLT

public boolean originalLexLT

Constructor Detail

LexOrder

public LexOrder(IntVar[] x,
                IntVar[] y)

It creates a lexicographical order for vectors x and y,

vectors x and y does not need to be of the same size. boolean lt defines if we require strict order, Lex_{<} (lt = true) or Lex_{=<} (lt = false).

Parameters:

x - first vector constrained by LexOrder constraint.

y - second vector constrained by LexOrder constraint.

LexOrder

public LexOrder(IntVar[] x,
                IntVar[] y,
                boolean lt)

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.

getDefaultConsistencyPruningEvent

public int getDefaultConsistencyPruningEvent()

Specified by:

getDefaultConsistencyPruningEvent in class 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.

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.

removeLevelLate

public void removeLevelLate(int level)

Description copied from interface: RemoveLevelLate

This function is called in case of the backtrack. It is called after all timestamps, variables, mutablevariables have reverted to their values *after* removing the level.

Specified by:

removeLevelLate in interface RemoveLevelLate

Parameters:

level - the level which is being removed.

toString

public String toString()

Description copied from class: Constraint

It produces a string representation of a constraint state.

Overrides:

toString in class Constraint

establishGACInit

protected void establishGACInit()

updateAlpha

public void updateAlpha()

updateBeta

public void updateBeta(int i)