source: branches/OKBJavaConnector/ECJClient/src/ec/multiobjective/spea2/SPEA2Breeder.java @ 6152

/*
  Portions copyright 2010 by Sean Luke, Robert Hubley, and George Mason University
  Licensed under the Academic Free License version 3.0
  See the file "LICENSE" for more information
*/

package ec.multiobjective.spea2;

import ec.*;
import ec.util.*;
import ec.multiobjective.*;
import ec.simple.*;
import java.util.*;

/* 
 * SPEA2Breeder.java
 * 
 * Created: Sat Oct 16 11:24:43 EDT 2010
 * By: Faisal Abidi and Sean Luke
 * Replaces earlier class by: Robert Hubley, with revisions by Gabriel Balan and Keith Sullivan
 */

/**
 * This subclass of SimpleBreeder overrides the loadElites method to build an archive in the top elites[subpopnum]
 * of each subpopulation.  It computes the sparsity metric, then constructs the archive.
 */

public class SPEA2Breeder extends SimpleBreeder
    {
    protected void loadElites(EvolutionState state, Population newpop)
        {
        // are our elites small enough?
        for(int x=0;x<state.population.subpops.length;x++)
            if (elite[x]>state.population.subpops[x].individuals.length)
                state.output.error("The number of elites for subpopulation " + x + " exceeds the actual size of the subpopulation", new Parameter(EvolutionState.P_BREEDER).push(P_ELITE).push(""+x));
        state.output.exitIfErrors();

        // do it
        for (int sub = 0; sub < state.population.subpops.length; sub++)
            {
            Individual[] newInds = newpop.subpops[sub].individuals;  // The new population after we are done picking the elites                 
            Individual[] oldInds = state.population.subpops[sub].individuals;   // The old population from which to pick elites
                        
            buildArchive(state, oldInds, newInds, elite[sub]);
            }

        // optionally force reevaluation
        unmarkElitesEvaluated(newpop);
        }

    public double[] calculateDistancesFromIndividual(Individual ind, Individual[] inds)
        {
        double[] d = new double[inds.length];
        for(int i = 0; i < inds.length; i++)
            d[i] = ((SPEA2MultiObjectiveFitness)ind.fitness).sumSquaredObjectiveDistance((SPEA2MultiObjectiveFitness)inds[i].fitness);
        // now sort
        Arrays.sort(d);
        return d;
        }


    public void buildArchive(EvolutionState state, Individual[] oldInds, Individual[] newInds, int archiveSize)
        {
        Individual[] dummy = new Individual[0];
                
        // step 1: load the archive with the pareto-nondominated front
        ArrayList archive = new ArrayList();
        ArrayList nonFront = new ArrayList();
        MultiObjectiveFitness.partitionIntoParetoFront(oldInds, archive, nonFront);
        int currentArchiveSize = archive.size();
                
        // step 2: if the archive isn't full, load the remainder with the fittest individuals (using customFitnessMetric) that aren't in the archive yet
        if (currentArchiveSize < archiveSize)
            {
            Collections.sort(nonFront);  // the fitter individuals will be earlier
            int len = (archiveSize - currentArchiveSize);
            for(int i = 0; i < len; i++)
                {
                archive.add(nonFront.get(i));
                currentArchiveSize++;
                }
            }
                        

        // step 3: if the archive is OVERFULL, iterate as follows:
        //              step 3a: remove the k-closest individual in the archive
        SPEA2Evaluator evaluator = ((SPEA2Evaluator)(state.evaluator));
        Individual[] inds = (Individual[])(archive.toArray(dummy));
                
        while(currentArchiveSize > archiveSize)
            {
            Individual closest = (Individual)(archive.get(0));
            int closestIndex = 0;
            double[] closestD = calculateDistancesFromIndividual(closest, oldInds);
                        
            for(int i = 1; i < currentArchiveSize; i++)
                {
                Individual competitor = (Individual)(archive.get(i));
                double[] competitorD = calculateDistancesFromIndividual(competitor, oldInds);
                                
                for(int k = 0; k < oldInds.length; k++)
                    {
                    if (closestD[i] > competitorD[i])
                        { closest = competitor ; closestD = competitorD;  closestIndex = k; break; }
                    else if (closestD[i] < competitorD[i])
                        { break; }
                    }
                }
                        
            // remove him destructively -- put the top guy in his place and remove the top guy.  This is O(1)
            archive.set(closestIndex, archive.get(archive.size()-1));
            archive.remove(archive.size()-1);
                        
            currentArchiveSize--;
            }
                                                
        // step 4: put clones of the archive in the new individuals
        Object[] obj = archive.toArray();
        for(int i = 0; i < archiveSize; i++)
            newInds[newInds.length - archiveSize + i] = (Individual)(((Individual)obj[i]).clone());
        }
    }