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VarOrderHeap.java

/*******************************************************************************
* SAT4J: a SATisfiability library for Java Copyright (C) 2004-2008 Daniel Le Berre
*
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU Lesser General Public License Version 2.1 or later (the
* "LGPL"), in which case the provisions of the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of the LGPL, and not to allow others to use your version of
* this file under the terms of the EPL, indicate your decision by deleting
* the provisions above and replace them with the notice and other provisions
* required by the LGPL. If you do not delete the provisions above, a recipient
* may use your version of this file under the terms of the EPL or the LGPL.
* 
* Based on the original MiniSat specification from:
* 
* An extensible SAT solver. Niklas Een and Niklas Sorensson. Proceedings of the
* Sixth International Conference on Theory and Applications of Satisfiability
* Testing, LNCS 2919, pp 502-518, 2003.
*
* See www.minisat.se for the original solver in C++.
* 
*******************************************************************************/
package org.sat4j.minisat.orders;

import static org.sat4j.core.LiteralsUtils.var;

import java.io.PrintWriter;
import java.io.Serializable;

import org.sat4j.minisat.core.Heap;
import org.sat4j.minisat.core.ILits;
import org.sat4j.minisat.core.IOrder;
import org.sat4j.minisat.core.IPhaseSelectionStrategy;

/*
 * Created on 16 oct. 2003
 */

/**
 * @author leberre Heuristique du prouveur. Changement par rapport au MiniSAT
 *         original : la gestion activity est faite ici et non plus dans Solver.
 */
00048 public class VarOrderHeap<L extends ILits> implements IOrder<L>, Serializable {

    private static final long serialVersionUID = 1L;

    private static final double VAR_RESCALE_FACTOR = 1e-100;

    private static final double VAR_RESCALE_BOUND = 1 / VAR_RESCALE_FACTOR;

    /**
     * mesure heuristique de l'activite d'une variable.
     */
00059     protected double[] activity = new double[1];

    private double varDecay = 1.0;

    /**
     * increment pour l'activite des variables.
     */
00066     private double varInc = 1.0;

    protected L lits;

    private long nullchoice = 0;

    protected Heap heap;

    protected IPhaseSelectionStrategy phaseStrategy;
    
    public VarOrderHeap() {
        this(new PhaseInLastLearnedClauseSelectionStrategy());
    }
    
    public VarOrderHeap(IPhaseSelectionStrategy strategy) {
        this.phaseStrategy = strategy;
    }
    
    /**
     * Change the selection strategy.
     * 
     * @param strategy
     */
00089     public void setPhaseSelectionStrategy(IPhaseSelectionStrategy strategy) {
        phaseStrategy = strategy;
    }
    
    public IPhaseSelectionStrategy getPhaseSelectionStrategy() {
        return phaseStrategy;
    }
    
    public void setLits(L lits) {
        this.lits = lits;
    }

    /**
     * Selectionne une nouvelle variable, non affectee, ayant l'activite
     * la plus elevee.
     * 
     * @return Lit.UNDEFINED si aucune variable n'est trouvee
     */
00107     public int select() {
        while (!heap.empty()) {
            int var = heap.getmin();
            int next = phaseStrategy.select(var);
            if (lits.isUnassigned(next)) {
                if (activity[var] < 0.0001) {
                    nullchoice++;
                }
                return next;
            }
        }
        return ILits.UNDEFINED;
    }

    /**
     * Change la valeur de varDecay.
     * 
     * @param d
     *            la nouvelle valeur de varDecay
     */
00127     public void setVarDecay(double d) {
        varDecay = d;
    }

    /**
     * Methode appelee quand la variable x est desaffectee.
     * 
     * @param x
     */
00136     public void undo(int x) {
        if (!heap.inHeap(x))
            heap.insert(x);
    }

    /**
     * Appelee lorsque l'activite de la variable x a change.
     * 
     * @param p
     *            a literal
     */
00147     public void updateVar(int p) {
        int var = var(p);
        updateActivity(var);
        phaseStrategy.updateVar(p);
        if (heap.inHeap(var))
            heap.increase(var);
    }

    protected void updateActivity(final int var) {
        if ((activity[var] += varInc) > VAR_RESCALE_BOUND) {
            varRescaleActivity();
        }
    }

    /**
     * 
     */
    public void varDecayActivity() {
        varInc *= varDecay;
    }

    /**
     * 
     */
    private void varRescaleActivity() {
        for (int i = 1; i < activity.length; i++) {
            activity[i] *= VAR_RESCALE_FACTOR;
        }
        varInc *= VAR_RESCALE_FACTOR;
    }

    public double varActivity(int p) {
        return activity[var(p)];
    }

    /**
     * 
     */
    public int numberOfInterestingVariables() {
        int cpt = 0;
        for (int i = 1; i < activity.length; i++) {
            if (activity[i] > 1.0) {
                cpt++;
            }
        }
        return cpt;
    }

    /**
     * that method has the responsability to initialize all arrays in the
     * heuristics. PLEASE CALL super.init() IF YOU OVERRIDE THAT METHOD.
     */
00199     public void init() {
        int nlength = lits.nVars() + 1;
        activity = new double[nlength];
        phaseStrategy.init(nlength);
        activity[0] = -1;
        heap = new Heap(activity);
        heap.setBounds(nlength);
        for (int i = 1; i < nlength; i++) {
            assert i > 0;
            assert i <= lits.nVars() : "" + lits.nVars() + "/" + i; //$NON-NLS-1$ //$NON-NLS-2$
            activity[i] = 0.0;
            if (lits.belongsToPool(i)) {
                heap.insert(i);
            }
        }
    }

    @Override
    public String toString() {
        return "VSIDS like heuristics from MiniSAT using a heap "+phaseStrategy; //$NON-NLS-1$
    }

    public ILits getVocabulary() {
        return lits;
    }

    public void printStat(PrintWriter out, String prefix) {
        out.println(prefix + "non guided choices\t" + nullchoice); //$NON-NLS-1$
    }

    public void assignLiteral(int p) {
        // do nothing       
    }
}

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