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/*******************************************************************************
* Copyright (c) 2010-2016, Andras Szabolcs Nagy, Zoltan Ujhelyi and Daniel Varro
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v. 2.0 which is available at
* http://www.eclipse.org/legal/epl-v20.html.
*
* SPDX-License-Identifier: EPL-2.0
*******************************************************************************/
package org.eclipse.viatra.dse.api.strategy.impl;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Random;
import java.util.concurrent.atomic.AtomicBoolean;
import org.apache.log4j.Logger;
import org.eclipse.viatra.dse.api.strategy.interfaces.IStrategy;
import org.eclipse.viatra.dse.base.ThreadContext;
import org.eclipse.viatra.dse.objectives.Fitness;
import org.eclipse.viatra.dse.objectives.ObjectiveComparatorHelper;
import org.eclipse.viatra.dse.objectives.TrajectoryFitness;
public class HillClimbingStrategy implements IStrategy {
private AtomicBoolean isInterrupted = new AtomicBoolean(false);
private ThreadContext context;
private Logger logger = Logger.getLogger(IStrategy.class);
private Random random = new Random();
private double percentOfOpenedStates;
private ObjectiveComparatorHelper objectiveComparatorHelper;
public HillClimbingStrategy() {
this(2);
}
public HillClimbingStrategy(double percentOfOpenedStates) {
this.percentOfOpenedStates = percentOfOpenedStates;
}
@Override
public void initStrategy(ThreadContext context) {
this.context = context;
objectiveComparatorHelper = context.getObjectiveComparatorHelper();
logger.info("Hill climbing exploration strategy is initied.");
}
@Override
public void explore() {
boolean globalConstraintsAreSatisfied = context.checkGlobalConstraints();
if (!globalConstraintsAreSatisfied) {
boolean isSuccessfulUndo = context.backtrack();
if (!isSuccessfulUndo) {
logger.info("Global contraint is not satisifed and cannot backtrack.");
return;
}
}
mainloop: do {
Fitness previousFitness = context.calculateFitness();
logger.debug("Current depth: " + context.getDepth() + " Fitness: " + previousFitness);
Collection<Object> transitionsFromCurrentState = context.getCurrentActivationIds();
while (transitionsFromCurrentState.isEmpty()) {
logger.debug("No transitions from current state: considered as a solution.");
saveSolutionAndBacktrack();
continue mainloop;
}
ArrayList<Object> transitionsToTry = new ArrayList<>(transitionsFromCurrentState.size());
for (Object transition : transitionsFromCurrentState) {
transitionsToTry.add(transition);
}
double numberOfTransitionsToTry = transitionsToTry.size() * percentOfOpenedStates;
for (; numberOfTransitionsToTry > 0 && !transitionsToTry.isEmpty(); numberOfTransitionsToTry--) {
int index = random.nextInt(transitionsToTry.size());
Object transition = transitionsToTry.remove(index);
context.executeAcitvationId(transition);
if (!context.checkGlobalConstraints()) {
logger.debug("Global contraint is not satisifed, backtrack.");
context.backtrack();
continue;
}
if (context.isCurrentStateInTrajectory()) {
logger.debug("Current state is in trajectory, backtrack.");
context.backtrack();
continue;
}
Fitness fitness = context.calculateFitness();
objectiveComparatorHelper.addTrajectoryFitness(
new TrajectoryFitness(context.getTrajectoryInfo().getLastActivationId(), fitness));
context.backtrack();
}
if (objectiveComparatorHelper.getTrajectoryFitnesses().isEmpty()) {
logger.debug("No viable transitions from current state: considered as a solution.");
saveSolutionAndBacktrack();
continue;
}
TrajectoryFitness randomBestFitness = objectiveComparatorHelper.getRandomBest();
objectiveComparatorHelper.clearTrajectoryFitnesses();
int compare = objectiveComparatorHelper.compare(previousFitness, randomBestFitness.fitness);
if (compare > 0) {
saveSolutionAndBacktrack();
continue;
} else {
previousFitness = randomBestFitness.fitness;
Object transition = randomBestFitness.trajectory[randomBestFitness.trajectory.length - 1];
context.executeAcitvationId(transition);
}
} while (!isInterrupted.get());
logger.info("Terminated.");
}
private void saveSolutionAndBacktrack() {
context.calculateFitness();
context.newSolution();
logger.debug("Found solution: " + context.getTrajectoryInfo().toString());
logger.debug("Backtrack for more solutions, if needed.");
context.backtrackUntilRoot();
}
@Override
public void interruptStrategy() {
isInterrupted.set(true);
}
}
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