/*
* Copyright 2010 JBoss Inc
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.drools.planner.core.localsearch.decider.acceptor.simulatedannealing;
import org.drools.planner.core.localsearch.scope.LocalSearchMoveScope;
import org.drools.planner.core.localsearch.scope.LocalSearchSolverPhaseScope;
import org.drools.planner.core.localsearch.scope.LocalSearchStepScope;
import org.drools.planner.core.localsearch.decider.acceptor.AbstractAcceptor;
import org.drools.planner.core.score.Score;
/**
* The time gradient implementation of simulated annealing.
*/
public class SimulatedAnnealingAcceptor extends AbstractAcceptor {
protected Score startingTemperature;
protected int levelsLength = -1;
protected double[] startingTemperatureLevels;
// No protected Score temperature do avoid rounding errors when using Score.multiply(double)
protected double[] temperatureLevels;
protected double temperatureMinimum = 1.0E-100; // Double.MIN_NORMAL is E-308
public void setStartingTemperature(Score startingTemperature) {
this.startingTemperature = startingTemperature;
}
// ************************************************************************
// Worker methods
// ************************************************************************
@Override
public void phaseStarted(LocalSearchSolverPhaseScope phaseScope) {
super.phaseStarted(phaseScope);
for (double startingTemperatureLevel : startingTemperature.toDoubleLevels()) {
if (startingTemperatureLevel < 0.0) {
throw new IllegalArgumentException("The startingTemperature (" + startingTemperature
+ ") cannot have negative level (" + startingTemperatureLevel + ").");
}
}
startingTemperatureLevels = startingTemperature.toDoubleLevels();
temperatureLevels = startingTemperatureLevels;
levelsLength = startingTemperatureLevels.length;
}
@Override
public void phaseEnded(LocalSearchSolverPhaseScope phaseScope) {
super.phaseEnded(phaseScope);
startingTemperatureLevels = null;
temperatureLevels = null;
levelsLength = -1;
}
public boolean isAccepted(LocalSearchMoveScope moveScope) {
LocalSearchSolverPhaseScope localSearchSolverPhaseScope = moveScope.getStepScope().getPhaseScope();
Score lastStepScore = localSearchSolverPhaseScope.getLastCompletedStepScope().getScore();
Score moveScore = moveScope.getScore();
if (moveScore.compareTo(lastStepScore) >= 0) {
return true;
}
Score scoreDifference = lastStepScore.subtract(moveScore);
double acceptChance = 1.0;
double[] scoreDifferenceLevels = scoreDifference.toDoubleLevels();
for (int i = 0; i < levelsLength; i++) {
double scoreDifferenceLevel = scoreDifferenceLevels[i];
double temperatureLevel = temperatureLevels[i];
double acceptChanceLevel;
if (scoreDifferenceLevel <= 0.0) {
// In this level moveScore is better than the lastStepScore, so do not disrupt the acceptChance
acceptChanceLevel = 1.0;
} else {
acceptChanceLevel = Math.exp(-scoreDifferenceLevel / temperatureLevel);
}
acceptChance *= acceptChanceLevel;
}
if (moveScope.getWorkingRandom().nextDouble() < acceptChance) {
return true;
} else {
return false;
}
}
@Override
public void stepEnded(LocalSearchStepScope stepScope) {
super.stepEnded(stepScope);
double timeGradient = stepScope.getTimeGradient();
double reverseTimeGradient = 1.0 - timeGradient;
temperatureLevels = new double[levelsLength];
for (int i = 0; i < levelsLength; i++) {
temperatureLevels[i] = startingTemperatureLevels[i] * reverseTimeGradient;
if (temperatureLevels[i] < temperatureMinimum) {
temperatureLevels[i] = temperatureMinimum;
}
}
// TODO implement reheating
}
}