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A collection of equivalence oracles
/* Copyright (C) 2013-2018 TU Dortmund
* This file is part of LearnLib, http://www.learnlib.de/.
*
* 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 de.learnlib.oracle.equivalence.mealy;
import java.util.Collection;
import java.util.List;
import java.util.Random;
import de.learnlib.api.SUL;
import de.learnlib.api.oracle.EquivalenceOracle.MealyEquivalenceOracle;
import de.learnlib.api.query.DefaultQuery;
import net.automatalib.automata.transout.MealyMachine;
import net.automatalib.commons.util.collections.CollectionsUtil;
import net.automatalib.words.Word;
import net.automatalib.words.WordBuilder;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Performs a random walk over the hypothesis. A random walk restarts with a fixed probability after every step and
* terminates after a fixed number of steps or with a counterexample. The number of steps to termination may be reset
* for every new search.
*
* @param
* input symbol type
* @param
* output symbol type
*
* @author falkhowar
*/
public class RandomWalkEQOracle implements MealyEquivalenceOracle {
private static final Logger LOGGER = LoggerFactory.getLogger(RandomWalkEQOracle.class);
/**
* probability to restart before step.
*/
private final double restartProbability;
/**
* maximum number of steps.
*/
private final long maxSteps;
/**
* RNG.
*/
private final Random random;
/**
* System under learning.
*/
private final SUL sul;
/**
* step counter.
*/
private long steps;
/**
* flag for reseting step count after every search.
*/
private boolean resetStepCount;
public RandomWalkEQOracle(SUL sul,
double restartProbability,
long maxSteps,
boolean resetStepCount,
Random random) {
this(sul, restartProbability, maxSteps, random);
this.resetStepCount = resetStepCount;
}
public RandomWalkEQOracle(SUL sul,
double restartProbability,
long maxSteps,
Random random) {
this.restartProbability = restartProbability;
this.maxSteps = maxSteps;
this.random = random;
this.sul = sul;
}
@Override
public DefaultQuery> findCounterExample(MealyMachine hypothesis,
Collection inputs) {
return doFindCounterExample(hypothesis, inputs);
}
private DefaultQuery> doFindCounterExample(MealyMachine hypothesis,
Collection inputs) {
// reset termination counter?
if (resetStepCount) {
steps = 0;
}
if (inputs.isEmpty()) {
LOGGER.warn("Passed empty set of inputs to equivalence oracle; no counterexample can be found!");
return null;
}
List choices = CollectionsUtil.randomAccessList(inputs);
int bound = choices.size();
S cur = hypothesis.getInitialState();
WordBuilder wbIn = new WordBuilder<>();
WordBuilder wbOut = new WordBuilder<>();
boolean first = true;
sul.pre();
try {
while (steps < maxSteps) {
if (first) {
first = false;
} else {
// restart?
double restart = random.nextDouble();
if (restart < restartProbability) {
sul.post();
sul.pre();
cur = hypothesis.getInitialState();
wbIn.clear();
wbOut.clear();
first = true;
}
}
// step
steps++;
I in = choices.get(random.nextInt(bound));
O outSul;
outSul = sul.step(in);
T hypTrans = hypothesis.getTransition(cur, in);
O outHyp = hypothesis.getTransitionOutput(hypTrans);
wbIn.add(in);
wbOut.add(outSul);
// ce?
if (!outSul.equals(outHyp)) {
DefaultQuery> ce = new DefaultQuery<>(wbIn.toWord());
ce.answer(wbOut.toWord());
return ce;
}
cur = hypothesis.getSuccessor(cur, in);
}
return null;
} finally {
sul.post();
}
}
}