uniol.apt.analysis.isomorphism.IsomorphismLogic.java Source code

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Here is the source code for uniol.apt.analysis.isomorphism.IsomorphismLogic.java

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/*-
 * APT - Analysis of Petri Nets and labeled Transition systems
 * Copyright (C) 2017  Uli Schlachter
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

package uniol.apt.analysis.isomorphism;

import java.util.ArrayDeque;
import java.util.Queue;
import java.util.Set;

import org.apache.commons.collections4.BidiMap;
import org.apache.commons.collections4.bidimap.DualHashBidiMap;
import static org.apache.commons.collections4.bidimap.UnmodifiableBidiMap.unmodifiableBidiMap;

import uniol.apt.adt.ts.Arc;
import uniol.apt.adt.ts.State;
import uniol.apt.adt.ts.TransitionSystem;
import uniol.apt.analysis.deterministic.Deterministic;
import uniol.apt.analysis.totallyreachable.TotallyReachable;
import uniol.apt.util.Pair;
import uniol.apt.util.interrupt.InterrupterRegistry;

/**
 * Check if two transition systems are isomorphic. Optionally, it is possible to ignore edge labels or require them to
 * be the same in both parts.
 *
 * @author Uli Schlachter
 */
public class IsomorphismLogic {
    private final BidiMap<State, State> isomorphism;

    /**
     * Constructor for testing if two labelled transition systems are isomorphic.
     *
     * @param lts1 The first LTS to test.
     * @param lts2 The second LTS to test.
     * @param checkLabels If true, "strong isomorphism" is tested and labels have to be identical between the LTS.
     *                    Otherwise labels are ignored.
     */
    public IsomorphismLogic(TransitionSystem lts1, TransitionSystem lts2, boolean checkLabels) {
        isomorphism = construct(lts1, lts2, checkLabels);
    }

    private static BidiMap<State, State> construct(TransitionSystem lts1, TransitionSystem lts2,
            boolean checkLabels) {
        // Check trivial case
        if (lts1.getNodes().size() != lts2.getNodes().size()) {
            return new DualHashBidiMap<>();
        }

        if (checkLabels) {
            boolean precond1 = checkPreconditions(lts1);
            boolean precond2 = checkPreconditions(lts2);
            if (precond1 != precond2)
                // Not isomorphic
                return new DualHashBidiMap<>();

            if (precond1 && precond2)
                // Both lts are totally reachable and deterministic. We can apply a special algorithm.
                return checkViaDepthSearch(lts1, lts2);
        }

        return new IsomorphismLogicComplex(lts1, lts2, checkLabels).getIsomorphism();
    }

    private static boolean checkPreconditions(TransitionSystem lts) {
        return new Deterministic(lts).isDeterministic() && new TotallyReachable(lts).isTotallyReachable();
    }

    private static BidiMap<State, State> checkViaDepthSearch(TransitionSystem lts1, TransitionSystem lts2) {
        BidiMap<State, State> result = new DualHashBidiMap<>();
        Set<String> alphabet = lts1.getAlphabet();
        if (!alphabet.equals(lts2.getAlphabet()))
            // Not isomorphic, there is an arc with a label not occurring in the other lts
            return result;

        Queue<Pair<State, State>> unhandled = new ArrayDeque<>();
        visit(result, unhandled, lts1.getInitialState(), lts2.getInitialState());

        while (!unhandled.isEmpty()) {
            InterrupterRegistry.throwIfInterruptRequestedForCurrentThread();

            Pair<State, State> pair = unhandled.remove();
            State state1 = pair.getFirst();
            State state2 = pair.getSecond();

            for (String label : alphabet) {
                State follow1 = follow(state1, label);
                State follow2 = follow(state2, label);

                if (!visit(result, unhandled, follow1, follow2))
                    // Not isomorphic
                    return new DualHashBidiMap<>();
            }
        }

        return result;
    }

    private static State follow(State state, String label) {
        Set<Arc> postset = state.getPostsetEdgesByLabel(label);
        assert postset.isEmpty() || postset.size() == 1 : "A deterministic LTS is not deterministic?";
        for (Arc arc : postset)
            return arc.getTarget();
        return null;
    }

    private static boolean visit(BidiMap<State, State> partialIsomorphism, Queue<Pair<State, State>> unhandled,
            State state1, State state2) {
        if (state1 == null && state2 == null)
            // Nothing to do
            return true;

        if (state1 == null || state2 == null)
            // Not isomorphic
            return false;

        State oldState1 = partialIsomorphism.getKey(state2);
        if (state1.equals(oldState1))
            // This mapping was already known
            return true;
        if (oldState1 != null)
            // We have a conflicting mapping!
            return false;

        State oldState2 = partialIsomorphism.put(state1, state2);
        if (oldState2 != null) {
            // If this assert fails, then state1 was already mapped to state2 before. However, we already
            // checked for this case above.
            assert !state2.equals(oldState2);

            // We have a conflicting mapping!
            return false;
        }

        unhandled.add(new Pair<State, State>(state1, state2));
        return true;
    }

    /**
     * Returns result of algorithm.
     * @return True if the inputs are isomorphic to each other
     */
    public boolean isIsomorphic() {
        return !isomorphism.isEmpty();
    }

    public BidiMap<State, State> getIsomorphism() {
        return unmodifiableBidiMap(isomorphism);
    }
}

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