Max Fitness 在遗传算法实现中停留在局部最大值

Question

下面这段代码有问题。它是种群进化的实现。在我的例子中，最大适应度每次都达到局部最大值并且无法达到最大可能值。请提出必要的修改建议并说明理由。

Individual.java

package genetic.algorithm.project;

import java.util.Random;

public class Individual {

    public static int SIZE = 300;
    private int[] genes = new int[SIZE];
    private double fitnessValue = 0.0;


    // Getters and Setters
    public void setGene(int index,int gene){
        this.genes[index] = gene;
    }

    public int getGene(int index){
        return this.genes[index];
    }

    public void setFitnessValue(double fitness){
        this.fitnessValue = fitness;
    }

    public double getFitnessValue(){
        return this.fitnessValue;
    }

    //Function to generate a new individual with random set of genes
    public void generateIndividual(){
        Random rand = new Random();
        for(int i=0;i<SIZE;i++){
            this.setGene(i, rand.nextInt(2));
        }
    }

    //Mutation Function
    public void mutate(){
        Random rand = new Random();
        int index = rand.nextInt(SIZE);
        this.setGene(index, 1-this.getGene(index)); // Flipping value of gene 
    }

    //Function to set Fitness value of an individual
    public int evaluate(){

        int fitness = 0;
        for(int i=0; i<SIZE; ++i) {
            fitness += this.getGene(i);
        }
        this.setFitnessValue(fitness);
        return fitness;
    }

}

Population.java

import java.util.Random;

public class Population {

    final static int ELITISM = 1;
    final static int POP_SIZE = 200+ELITISM; //Population size + Elitism (1)
    final static int MAX_ITER = 2000;
    final static double MUTATION_RATE = 0.05;
    final static double CROSSOVER_RATE = 0.7;
    private static Random rand = new Random(); 

    private double totalFitness;
    private  Individual[] pop;

    //Constructor
    public Population(){
        pop = new Individual[POP_SIZE];
        //Initialising population
        for(int i=0;i<POP_SIZE;i++){
            pop[i] = new Individual();
            pop[i].generateIndividual();

        }
        this.evaluate();
    }

    //Storing new generation in population
    public void setPopulation(Individual[] newPop) {
        this.pop = newPop;
    }


    //Method to find total fitness of population
    public double evaluate(){
        this.totalFitness = 0.0;
        for (int i = 0; i < POP_SIZE; i++) {
            this.totalFitness +=  pop[i].evaluate();
        }


       return this.totalFitness;
    }


    //Getters
    public Individual getIndividual(int index) {
        return pop[index];
    }


    //Function to find fittest individual for elitism
    public Individual getFittest() {
        Individual fittest = pop[0];
        for (int i = 0; i < POP_SIZE; i++) {
            if (fittest.getFitnessValue() <= getIndividual(i).getFitnessValue()) {
                fittest = getIndividual(i);
            }
        }
        return fittest;
    }

    //CROSSOVER Function : Takes 2 individuals and returns 2 new individuals
    public static Individual[] crossover(Individual indiv1,Individual indiv2) {
        Individual[] newIndiv = new Individual[2];
        newIndiv[0] = new Individual();
        newIndiv[1] = new Individual();
        int randPoint = rand.nextInt(Individual.SIZE);
        int i;
        for (i=0; i<randPoint; ++i) {
            newIndiv[0].setGene(i, indiv1.getGene(i));
            newIndiv[1].setGene(i, indiv2.getGene(i));
        }
        for (; i<Individual.SIZE; ++i) {
            newIndiv[0].setGene(i, indiv2.getGene(i));
            newIndiv[1].setGene(i, indiv1.getGene(i));
        }

        return newIndiv;
    }

    //Roulette Wheel Selection Function
    public Individual rouletteWheelSelection() {

        double randNum = rand.nextDouble() * this.totalFitness;
        int idx;

        for (idx=0; idx<POP_SIZE && randNum>0; idx++) {
            randNum -= pop[idx].getFitnessValue();
        }
        return pop[idx-1];
    }

    //Main method
    public static void main(String[] args) {
        Population pop = new Population();
        Individual[] newPop = new Individual[POP_SIZE];
        Individual[] indiv = new Individual[2];
        //Current Population Stats
        System.out.println("Total Fitness = "+pop.totalFitness);
        System.out.println("Best  Fitness = "+pop.getFittest().getFitnessValue());

        int count;
        for(int iter=0;iter<MAX_ITER;iter++){
            count =0;

                //Elitism
                newPop[count] = pop.getFittest();
                count++;

           //Creating new population
            while(count < POP_SIZE){
                //Selecting parents
                indiv[0] = pop.rouletteWheelSelection();
                indiv[1] = pop.rouletteWheelSelection();

                // Crossover
                if (rand.nextDouble() < CROSSOVER_RATE ) {
                    indiv = crossover(indiv[0], indiv[1]);
                }

                // Mutation
                if ( rand.nextDouble() < MUTATION_RATE ) {
                    indiv[0].mutate();
                }
                if ( rand.nextDouble() < MUTATION_RATE ) {
                    indiv[1].mutate();
                }

                // add to new population
                newPop[count] = indiv[0];
                newPop[count+1] = indiv[1];
                count += 2;
            }
            // Saving new population in pop
            pop.setPopulation(newPop);
            //Evaluating new population
            pop.evaluate();
            System.out.print("Total Fitness = " + pop.totalFitness);
            System.out.println(" ; Best Fitness = " +pop.getFittest().getFitnessValue()); 

        }
        Individual bestIndiv = pop.getFittest();
    }

}

在我的例子中，适应度的最大可能值为 300，但它始终停留在 200-230 左右。

Answer 1

替换了这个函数：

public void setPopulation(Individual[] newPop) {
    this.pop = newPop;
}

和

public void setPopulation(Individual[] newPop) {
    System.arraycopy(newPop, 0, this.pop, 0, POP_SIZE);
}

现在可以正常使用了。