/*
* 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.LocalSearchSolverScope;
import org.drools.planner.core.localsearch.LocalSearchStepScope;
import org.drools.planner.core.localsearch.decider.MoveScope;
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 partsLength;
protected double[] startingTemperatureParts;
// No protected Score temperature do avoid rounding errors when using Score.multiply(double)
protected double[] temperatureParts;
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 solvingStarted(LocalSearchSolverScope localSearchSolverScope) {
for (double startingTemperaturePart : startingTemperature.toDoubleArray()) {
if (startingTemperaturePart < 0.0) {
throw new IllegalArgumentException("The startingTemperature (" + startingTemperature
+ ") cannot have negative part (" + startingTemperaturePart + ").");
}
}
startingTemperatureParts = startingTemperature.toDoubleArray();
temperatureParts = startingTemperatureParts;
partsLength = startingTemperatureParts.length;
}
public double calculateAcceptChance(MoveScope moveScope) {
LocalSearchSolverScope localSearchSolverScope = moveScope.getLocalSearchStepScope().getLocalSearchSolverScope();
Score lastStepScore = localSearchSolverScope.getLastCompletedLocalSearchStepScope().getScore();
Score moveScore = moveScope.getScore();
if (moveScore.compareTo(lastStepScore) >= 0) {
return 1.0;
}
Score scoreDifference = lastStepScore.subtract(moveScore);
double acceptChance = 1.0;
double[] scoreDifferenceParts = scoreDifference.toDoubleArray();
for (int i = 0; i < partsLength; i++) {
double scoreDifferencePart = scoreDifferenceParts[i];
double temperaturePart = temperatureParts[i];
double acceptChancePart;
if (scoreDifferencePart <= 0.0) {
// In this part it is moveScore is better than the lastStepScore, so do not disrupt the acceptChance
acceptChancePart = 1.0;
} else {
acceptChancePart = Math.exp(-scoreDifferencePart / temperaturePart);
}
acceptChance *= acceptChancePart;
}
if (moveScope.getWorkingRandom().nextDouble() < acceptChance) {
return 1.0;
} else {
return 0.0;
}
}
@Override
public void stepTaken(LocalSearchStepScope localSearchStepScope) {
super.stepTaken(localSearchStepScope);
double timeGradient = localSearchStepScope.getTimeGradient();
double reverseTimeGradient = 1.0 - timeGradient;
temperatureParts = new double[partsLength];
for (int i = 0; i < partsLength; i++) {
temperatureParts[i] = startingTemperatureParts[i] * reverseTimeGradient;
if (temperatureParts[i] < temperatureMinimum) {
temperatureParts[i] = temperatureMinimum;
}
}
// TODO implement reheating
}
}