org.chocosolver.solver.search.strategy.selectors.variables

Class ImpactBased

java.lang.Object

org.chocosolver.solver.search.strategy.strategy.AbstractStrategy<IntVar>

org.chocosolver.solver.search.strategy.selectors.variables.ImpactBased

All Implemented Interfaces:

Serializable, ICause, IMonitorContradiction, IMonitorDownBranch, IMonitorRestart, ISearchMonitor

public class ImpactBased
extends AbstractStrategy<IntVar>
implements IMonitorDownBranch, IMonitorRestart, IMonitorContradiction, ICause

Implementation of the search described in: "Impact-Based Search Strategies for Constraint Programming", Philippe Refalo, CP2004.

Impacts of variables are first computed on initialisation, (only 3 values are tested for bounded variables); Ties are broken randomly.

Since:

21/09/12

Author:

Charles Prud'homme

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
protected int	aging
protected boolean	asgntFailed
protected int	currentVal
protected int	currentVar
protected double[][]	Ilabel
protected IntVar	lAfVar
protected boolean	learnsAndFails
protected int	nodeImpact
protected int[]	offsets
protected IStateDouble	searchSpaceSize
protected Solver	solver
protected int	split
protected long	timeLimit

Fields inherited from class org.chocosolver.solver.search.strategy.strategy.AbstractStrategy

LOGGER, vars

Constructor Summary

Constructors

Constructor and Description
ImpactBased(IntVar[] ivariables, int alpha, int split, int nodeImpact, long seed, boolean initOnly) Create an Impact-based search strategy with Node Impact strategy.

Method Summary

Methods

Modifier and Type	Method and Description
void	afterDownLeftBranch()
void	afterDownRightBranch()
void	afterRestart()
void	beforeDownLeftBranch()
void	beforeDownRightBranch()
void	beforeRestart()
Decision<IntVar>	computeDecision(IntVar variable) Computes a decision to be applied to variable var This method should be implemented in order to use search patterns
protected double	computeImpact(int idx) Compute the impact of a variable
Decision<IntVar>	getDecision() Provides access to the current decision in the strategy.
void	init() Prepare this to be used in a search loop
void	onContradiction(ContradictionException cex)
protected void	reevaluateImpact()
protected double	searchSpaceSize() Compute the search space size
void	setTimeLimit(long timeLimit)
protected void	updateImpact(double nImpact, int varIdx, int valIdx) Update the impact of an assignment I(v=a)
boolean	why(RuleStore ruleStore, IntVar var, IEventType evt, int value) Add new rules to the rule store

Methods inherited from class org.chocosolver.solver.search.strategy.strategy.AbstractStrategy

getVariables, toString

Methods inherited from class java.lang.Object

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

Field Detail

aging

protected final int aging

Ilabel

protected double[][] Ilabel

offsets

protected int[] offsets

split

protected int split

searchSpaceSize

protected IStateDouble searchSpaceSize

currentVar

protected int currentVar

currentVal

protected int currentVal

nodeImpact

protected int nodeImpact

solver

protected Solver solver

asgntFailed

protected boolean asgntFailed

learnsAndFails

protected boolean learnsAndFails

lAfVar

protected IntVar lAfVar

timeLimit

protected long timeLimit

Constructor Detail

ImpactBased

public ImpactBased(IntVar[] ivariables,
           int alpha,
           int split,
           int nodeImpact,
           long seed,
           boolean initOnly)

Create an Impact-based search strategy with Node Impact strategy.

"Impact-Based Search Strategies for Constraint Programming", Philippe Refalo, CP2004.

Parameters:

ivariables - variables of the problem (should be integers)

alpha - aging parameter

split - split parameter for subdomains computation

nodeImpact - force update of impacts every nodeImpact nodes. Set value to 0 to avoid using it.

seed - a seed for random

initOnly - only apply the initialisation phase, do not update impact thereafter

Method Detail

computeDecision

public Decision<IntVar> computeDecision(IntVar variable)

Description copied from class: AbstractStrategy

Computes a decision to be applied to variable var This method should be implemented in order to use search patterns

Overrides:

computeDecision in class AbstractStrategy<IntVar>

Parameters:

variable - a variable

Returns:

a decision to be applied to variable var

getDecision

public Decision<IntVar> getDecision()

Description copied from class: AbstractStrategy

Provides access to the current decision in the strategy. If there are no more decision to provide, it returns null.

Specified by:

getDecision in class AbstractStrategy<IntVar>

Returns:

the current decision

setTimeLimit

public void setTimeLimit(long timeLimit)

init

public void init()
          throws ContradictionException

Description copied from class: AbstractStrategy

Prepare this to be used in a search loop

Specified by:

init in class AbstractStrategy<IntVar>

Throws:

ContradictionException

beforeDownLeftBranch

public void beforeDownLeftBranch()

Specified by:

beforeDownLeftBranch in interface IMonitorDownBranch

afterDownLeftBranch

public void afterDownLeftBranch()

Specified by:

afterDownLeftBranch in interface IMonitorDownBranch

beforeDownRightBranch

public void beforeDownRightBranch()

Specified by:

beforeDownRightBranch in interface IMonitorDownBranch

afterDownRightBranch

public void afterDownRightBranch()

Specified by:

afterDownRightBranch in interface IMonitorDownBranch

onContradiction

public void onContradiction(ContradictionException cex)

Specified by:

onContradiction in interface IMonitorContradiction

computeImpact

protected double computeImpact(int idx)

Compute the impact of a variable

Parameters:

idx - index of the variable

Returns:

the impact of the variable idx

updateImpact

protected void updateImpact(double nImpact,
                int varIdx,
                int valIdx)

Update the impact of an assignment I(v=a)

Parameters:

nImpact - new impact

varIdx - index of the variable

valIdx - index of the value

searchSpaceSize

protected double searchSpaceSize()

Compute the search space size

Returns:

search space size

reevaluateImpact

protected void reevaluateImpact()

beforeRestart

public void beforeRestart()

Specified by:

beforeRestart in interface IMonitorRestart

afterRestart

public void afterRestart()

Specified by:

afterRestart in interface IMonitorRestart

why

public boolean why(RuleStore ruleStore,
          IntVar var,
          IEventType evt,
          int value)

Description copied from interface: ICause

Add new rules to the rule store

Specified by:

why in interface ICause

Parameters:

ruleStore - the rule store

var - the modified variable

evt - the undergoing event

value - the value (for REMOVE only)

Returns:

true if at least one rule has been added to the rule store