/**
* Copyright (c) 1999-2014, Ecole des Mines de Nantes
* All rights reserved.
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* * Neither the name of the Ecole des Mines de Nantes nor the
* names of its contributors may be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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/**
* Created by IntelliJ IDEA.
* User: Jean-Guillaume Fages
* Date: 23/05/12
* Time: 16:51
*/
package solver.search.loop.lns;
import solver.ICause;
import solver.Solver;
import solver.exception.ContradictionException;
import solver.explanations.Deduction;
import solver.explanations.Explanation;
import solver.search.loop.lns.neighbors.INeighbor;
import solver.search.loop.monitors.IMonitorInterruption;
import solver.search.loop.monitors.IMonitorRestart;
import solver.search.loop.monitors.IMonitorSolution;
/**
* How to branch a Large Neighborhood Search ?
* This class provides services to plug a LNS, it relies on a Neighbor computation, and enables fast restarts.
*/
public class LargeNeighborhoodSearch implements ICause, IMonitorSolution, IMonitorInterruption, IMonitorRestart {
//***********************************************************************************
// VARIABLES
//***********************************************************************************
protected Solver solver;
protected final INeighbor neighbor;
protected boolean hasAppliedNeighborhood;
//***********************************************************************************
// CONSTRUCTORS
//***********************************************************************************
public LargeNeighborhoodSearch(final Solver solver, INeighbor neighbor, final boolean restartAfterEachSolution) {
this.solver = solver;
this.neighbor = neighbor;
solver.plugMonitor(new IMonitorSolution() {
@Override
public void onSolution() {
if(restartAfterEachSolution){
solver.getSearchLoop().restart();
}
}
});
}
//***********************************************************************************
// RECORD & RESTART
//***********************************************************************************
@Override
public void onSolution() {
// the fast restart policy is plugged when the first solution has been found
if (solver.getMeasures().getSolutionCount() == 1) {
neighbor.activeFastRestart();
}
neighbor.recordSolution();
}
@Override
public void afterInterrupt() {
if (hasAppliedNeighborhood && solver.getMeasures().getSolutionCount() > 0 && !solver.getSearchLoop().hasReachedLimit() && !neighbor.isSearchComplete()) {
neighbor.restrictLess();
solver.getSearchLoop().forceAlive(true);
solver.getSearchLoop().restart();
}
}
//***********************************************************************************
// FIX VARIABLES FOR NEXT LNS STEP
//***********************************************************************************
@Override
public void beforeRestart() {
hasAppliedNeighborhood = false;
}
@Override
public void afterRestart() {
if (solver.getMeasures().getSolutionCount() > 0) {
try {
neighbor.fixSomeVariables(this);
hasAppliedNeighborhood = true;
solver.getEngine().propagate();
} catch (ContradictionException e) {
solver.getEngine().flush();
neighbor.restrictLess();
solver.getSearchLoop().restart();
}
}
}
@Override
public void explain(Deduction d, Explanation e) {}
}