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

package ec.multiobjective.nsga2;

import ec.*;
import ec.util.*;
import ec.simple.*;

/* 
 * NSGA2Breeder.java
 * 
 * Created: Thu Feb 04 2010
 * By: Faisal Abidi and Sean Luke
 */

/**
 * This SimpleBreeder subclass breeds a set of children from the Population, then
 * joins the original Population with the children in a (mu+mu) fashion.   An NSGA2Breeder
 * may have multiple threads for breeding.
 *
 * 
NSGA-II has fixed archive size (the population size), and so ignores the 'elites'
 * declaration.  However it will adhere to the 'reevaluate-elites' parameter in SimpleBreeder
 * to determine whether to force fitness reevaluation.

 */

public class NSGA2Breeder extends SimpleBreeder
    {
    public void setup(final EvolutionState state, final Parameter base)
        {
        super.setup(state, base);
        // make sure SimpleBreeder's elites facility isn't being used
        for (int i = 0; i < elite.length; i++)  // we use elite.length here instead of pop.subpops.length because the population hasn't been made yet.
            if (usingElitism(i))
                state.output.warning("You're using elitism with NSGA2Breeder, which is not permitted and will be ignored.  However the reevaluate-elites parameter *will* bre recognized by NSGAEvaluator.",
                    base.push(P_ELITE).push(""+i));

        if (sequentialBreeding) // uh oh, haven't tested with this
            state.output.fatal("NSGA2Breeder does not support sequential evaluation.",
                base.push(P_SEQUENTIAL_BREEDING));

        if (!clonePipelineAndPopulation)
            state.output.fatal("clonePipelineAndPopulation must be true for NSGA2Breeder.");
        }

    /**
     * Override breedPopulation(). We take the result from the super method in
     * SimpleBreeder and append it to the old population. Hence, after
     * generation 0, every subsequent call to
     * NSGA2Evaluator.evaluatePopulation() will be passed a
     * population of 2xoriginalPopSize individuals.
     */
    public Population breedPopulation(EvolutionState state)
        {
        Population oldPop = (Population) state.population;
        Population newPop = super.breedPopulation(state);
        Individual[] combinedInds;
        Subpopulation[] subpops = oldPop.subpops;
        Subpopulation oldSubpop;
        Subpopulation newSubpop;
        int subpopsLength = subpops.length;

        for (int i = 0; i < subpopsLength; i++)
            {
            oldSubpop = oldPop.subpops[i];
            newSubpop = newPop.subpops[i];
            combinedInds = new Individual[oldSubpop.individuals.length + newSubpop.individuals.length];
            System.arraycopy(newSubpop.individuals, 0, combinedInds, 0,  newSubpop.individuals.length);
            System.arraycopy(oldSubpop.individuals, 0, combinedInds,  newSubpop.individuals.length, oldSubpop.individuals.length);
            newSubpop.individuals = combinedInds;
            }
        return newPop;
        }
    }