protected IChromosome reAddFittest(Population a_pop, IChromosome a_fittest) {
   // Determine if all-time fittest chromosome is in the population.
   // --------------------------------------------------------------
   if (a_fittest != null && !a_pop.contains(a_fittest)) {
     // Re-add fittest chromosome to current population.
     // ------------------------------------------------
     a_pop.addChromosome(a_fittest);
     return a_fittest;
   }
   return null;
 }
 protected void updateChromosomes(Population a_pop, Configuration a_conf) {
   int currentPopSize = a_pop.size();
   // Ensure all chromosomes are updated.
   // -----------------------------------
   BulkFitnessFunction bulkFunction = a_conf.getBulkFitnessFunction();
   boolean bulkFitFunc = (bulkFunction != null);
   if (!bulkFitFunc) {
     for (int i = 0; i < currentPopSize; i++) {
       IChromosome chrom = a_pop.getChromosome(i);
       chrom.getFitnessValue();
     }
   }
 }
 /**
  * Cares that population size is kept constant and does not exceed the desired size.
  *
  * @param a_pop Population
  * @param a_conf Configuration
  */
 protected void keepPopSizeConstant(Population a_pop, Configuration a_conf) {
   if (a_conf.isKeepPopulationSizeConstant()) {
     try {
       a_pop.keepPopSizeConstant();
     } catch (InvalidConfigurationException iex) {
       throw new RuntimeException(iex);
     }
   }
 }
  /**
   * Evolves the population of chromosomes within a genotype. This will execute all of the genetic
   * operators added to the present active configuration and then invoke the natural selector to
   * choose which chromosomes will be included in the next generation population.
   *
   * @param a_pop the population to evolve
   * @param a_conf the configuration to use for evolution
   * @return evolved population
   * @author Klaus Meffert
   * @since 3.2
   */
  public Population evolve(Population a_pop, Configuration a_conf) {
    Population pop = a_pop;
    int originalPopSize = a_conf.getPopulationSize();
    boolean monitorActive = a_conf.getMonitor() != null;
    IChromosome fittest = null;
    // If first generation: Set age to one to allow genetic operations,
    // see CrossoverOperator for an illustration.
    // ----------------------------------------------------------------
    if (a_conf.getGenerationNr() == 0) {
      int size = pop.size();
      for (int i = 0; i < size; i++) {
        IChromosome chrom = pop.getChromosome(i);
        chrom.increaseAge();
      }
    } else {
      // Select fittest chromosome in case it should be preserved and we are
      // not in the very first generation.
      // -------------------------------------------------------------------
      if (a_conf.isPreserveFittestIndividual()) {
        /** @todo utilize jobs. In pop do also utilize jobs, especially for fitness computation */
        fittest = pop.determineFittestChromosome(0, pop.size() - 1);
      }
    }
    if (a_conf.getGenerationNr() > 0) {
      // Adjust population size to configured size (if wanted).
      // Theoretically, this should be done at the end of this method.
      // But for optimization issues it is not. If it is the last call to
      // evolve() then the resulting population possibly contains more
      // chromosomes than the wanted number. But this is no bad thing as
      // more alternatives mean better chances having a fit candidate.
      // If it is not the last call to evolve() then the next call will
      // ensure the correct population size by calling keepPopSizeConstant.
      // ------------------------------------------------------------------
      keepPopSizeConstant(pop, a_conf);
    }
    // Ensure fitness value of all chromosomes is udpated.
    // ---------------------------------------------------
    if (monitorActive) {
      // Monitor that fitness value of chromosomes is being updated.
      // -----------------------------------------------------------
      a_conf
          .getMonitor()
          .event(
              IEvolutionMonitor.MONITOR_EVENT_BEFORE_UPDATE_CHROMOSOMES1,
              a_conf.getGenerationNr(),
              new Object[] {pop});
    }
    updateChromosomes(pop, a_conf);
    if (monitorActive) {
      // Monitor that fitness value of chromosomes is being updated.
      // -----------------------------------------------------------
      a_conf
          .getMonitor()
          .event(
              IEvolutionMonitor.MONITOR_EVENT_AFTER_UPDATE_CHROMOSOMES1,
              a_conf.getGenerationNr(),
              new Object[] {pop});
    }
    // Apply certain NaturalSelectors before GeneticOperators will be executed.
    // ------------------------------------------------------------------------
    pop = applyNaturalSelectors(a_conf, pop, true);
    // Execute all of the Genetic Operators.
    // -------------------------------------
    applyGeneticOperators(a_conf, pop);
    // Reset fitness value of genetically operated chromosomes.
    // Normally, this should not be necessary as the Chromosome class
    // initializes each newly created chromosome with
    // FitnessFunction.NO_FITNESS_VALUE. But who knows which Chromosome
    // implementation is used...
    // ----------------------------------------------------------------
    int currentPopSize = pop.size();
    for (int i = originalPopSize; i < currentPopSize; i++) {
      IChromosome chrom = pop.getChromosome(i);
      chrom.setFitnessValueDirectly(FitnessFunction.NO_FITNESS_VALUE);
      // Mark chromosome as new-born.
      // ----------------------------
      chrom.resetAge();
      // Mark chromosome as being operated on.
      // -------------------------------------
      chrom.increaseOperatedOn();
    }
    // Increase age of all chromosomes which are not modified by genetic
    // operations.
    // -----------------------------------------------------------------
    int size = Math.min(originalPopSize, currentPopSize);
    for (int i = 0; i < size; i++) {
      IChromosome chrom = pop.getChromosome(i);
      chrom.increaseAge();
      // Mark chromosome as not being operated on.
      // -----------------------------------------
      chrom.resetOperatedOn();
    }
    // If a bulk fitness function has been provided, call it.
    // ------------------------------------------------------
    BulkFitnessFunction bulkFunction = a_conf.getBulkFitnessFunction();
    if (bulkFunction != null) {
      if (monitorActive) {
        // Monitor that bulk fitness will be called for evaluation.
        // --------------------------------------------------------
        a_conf
            .getMonitor()
            .event(
                IEvolutionMonitor.MONITOR_EVENT_BEFORE_BULK_EVAL,
                a_conf.getGenerationNr(),
                new Object[] {bulkFunction, pop});
      }
      /** @todo utilize jobs: bulk fitness function is not so important for a prototype! */
      bulkFunction.evaluate(pop);
      if (monitorActive) {
        // Monitor that bulk fitness has been called for evaluation.
        // ---------------------------------------------------------
        a_conf
            .getMonitor()
            .event(
                IEvolutionMonitor.MONITOR_EVENT_AFTER_BULK_EVAL,
                a_conf.getGenerationNr(),
                new Object[] {bulkFunction, pop});
      }
    }
    // Ensure fitness value of all chromosomes is udpated.
    // ---------------------------------------------------
    if (monitorActive) {
      // Monitor that fitness value of chromosomes is being updated.
      // -----------------------------------------------------------
      a_conf
          .getMonitor()
          .event(
              IEvolutionMonitor.MONITOR_EVENT_BEFORE_UPDATE_CHROMOSOMES2,
              a_conf.getGenerationNr(),
              new Object[] {pop});
    }
    updateChromosomes(pop, a_conf);
    if (monitorActive) {
      // Monitor that fitness value of chromosomes is being updated.
      // -----------------------------------------------------------
      a_conf
          .getMonitor()
          .event(
              IEvolutionMonitor.MONITOR_EVENT_AFTER_UPDATE_CHROMOSOMES2,
              a_conf.getGenerationNr(),
              new Object[] {pop});
    }
    // Apply certain NaturalSelectors after GeneticOperators have been applied.
    // ------------------------------------------------------------------------
    pop = applyNaturalSelectors(a_conf, pop, false);
    // Fill up population randomly if size dropped below specified percentage
    // of original size.
    // ----------------------------------------------------------------------
    if (a_conf.getMinimumPopSizePercent() > 0) {
      int sizeWanted = a_conf.getPopulationSize();
      int popSize;
      int minSize = (int) Math.round(sizeWanted * (double) a_conf.getMinimumPopSizePercent() / 100);
      popSize = pop.size();
      if (popSize < minSize) {
        IChromosome newChrom;
        IChromosome sampleChrom = a_conf.getSampleChromosome();
        Class sampleChromClass = sampleChrom.getClass();
        IInitializer chromIniter =
            a_conf.getJGAPFactory().getInitializerFor(sampleChrom, sampleChromClass);
        while (pop.size() < minSize) {
          try {
            /**
             * @todo utilize jobs as initialization may be time-consuming as invalid combinations
             *     may have to be filtered out
             */
            newChrom = (IChromosome) chromIniter.perform(sampleChrom, sampleChromClass, null);
            if (monitorActive) {
              // Monitor that fitness value of chromosomes is being updated.
              // -----------------------------------------------------------
              a_conf
                  .getMonitor()
                  .event(
                      IEvolutionMonitor.MONITOR_EVENT_BEFORE_ADD_CHROMOSOME,
                      a_conf.getGenerationNr(),
                      new Object[] {pop, newChrom});
            }
            pop.addChromosome(newChrom);
          } catch (Exception ex) {
            throw new RuntimeException(ex);
          }
        }
      }
    }
    IChromosome newFittest = reAddFittest(pop, fittest);
    if (monitorActive && newFittest != null) {
      // Monitor that fitness value of chromosomes is being updated.
      // -----------------------------------------------------------
      a_conf
          .getMonitor()
          .event(
              IEvolutionMonitor.MONITOR_EVENT_READD_FITTEST,
              a_conf.getGenerationNr(),
              new Object[] {pop, fittest});
    }

    // Increase number of generations.
    // -------------------------------
    a_conf.incrementGenerationNr();
    // Fire an event to indicate we've performed an evolution.
    // -------------------------------------------------------
    m_lastPop = pop;
    m_lastConf = a_conf;
    a_conf
        .getEventManager()
        .fireGeneticEvent(new GeneticEvent(GeneticEvent.GENOTYPE_EVOLVED_EVENT, this));
    return pop;
  }