nsgaii.java

关于多目标优化的代码

/**
 * NsgaII.java
 * @author Juan J. Durillo
 * @version 1.0  
 */
package jmetal.metaheuristics.nsgaII;

import jmetal.base.*;
import jmetal.qualityIndicator.QualityIndicator;
import jmetal.util.*;

/**
 * This class implements the NSGA-II algorithm. 
 */
public class NSGAII extends Algorithm {
  
  /**
   * stores the problem  to solve
   */
  private Problem  problem_;        
  
  /**
  * Constructor
  * @param problem Problem to solve
  */
  public NSGAII(Problem problem){
    this.problem_ = problem;                        
  } // NSGAII
  
  /**   
  * Runs the NSGA-II algorithm.
  * @return a <code>SolutionSet</code> that is a set of non dominated solutions
  * as a result of the algorithm execution  
   * @throws JMException 
  */  
  public SolutionSet execute() throws JMException {
    int populationSize ;
    int maxEvaluations ;
    int evaluations    ;
    
    QualityIndicator indicators          ; // QualityIndicator object
    int              requiredEvaluations ; // Use in the example of use of the
                                           // indicators object (see below)
    
    SolutionSet population          ;
    SolutionSet offspringPopulation ;
    SolutionSet union               ;
    
    Operator mutationOperator  ;
    Operator crossoverOperator ;
    Operator selectionOperator ;
    
    Distance distance = new Distance()  ;               
      
    //Read the parameters
    populationSize    = ((Integer)getInputParameter("populationSize")).intValue();
    maxEvaluations    = ((Integer)getInputParameter("maxEvaluations")).intValue();                
    indicators        = (QualityIndicator)getInputParameter("indicators") ;
      
    //Initialize the variables
    population  = new SolutionSet(populationSize);        
    evaluations = 0;         
    
    requiredEvaluations = 0 ;

    //Read the operators
    mutationOperator  = operators_.get("mutation");
    crossoverOperator = operators_.get("crossover");
    selectionOperator = operators_.get("selection");  

    // Create the initial solutionSet
    Solution newSolution;
    for (int i = 0; i < populationSize; i++) {
      newSolution = new Solution(problem_);                    
      problem_.evaluate(newSolution);            
      problem_.evaluateConstraints(newSolution);
      evaluations++;
      population.add(newSolution);
    } //for       
  
    // Generations ...
    while (evaluations < maxEvaluations) {
    
      // Create the offSpring solutionSet      
      offspringPopulation  = new SolutionSet(populationSize);        
      Solution [] parents = new Solution[2];
      for (int i = 0; i < (populationSize/2); i++){   
        //obtain parents
        parents[0] = (Solution)selectionOperator.execute(population);
        parents[1] = (Solution)selectionOperator.execute(population);
        if (evaluations < maxEvaluations) {                                
          Solution [] offSpring = (Solution []) crossoverOperator.execute(parents);                
          mutationOperator.execute(offSpring[0]);
          mutationOperator.execute(offSpring[1]);                
          problem_.evaluate(offSpring[0]);            
          problem_.evaluateConstraints(offSpring[0]);
          problem_.evaluate(offSpring[1]);  
          problem_.evaluateConstraints(offSpring[1]);            
          offspringPopulation.add(offSpring[0]);
          offspringPopulation.add(offSpring[1]);              
          evaluations += 2;
        } else {
          offspringPopulation.add(new Solution(parents[0]));
          offspringPopulation.add(new Solution(parents[1]));                
        } // if                            
      } // for
      

      // Create the solutionSet union of solutionSet and offSpring
      union = ((SolutionSet)population).union(offspringPopulation);              

      // Ranking the union
      Ranking ranking = new Ranking(union);                        

      int remain = populationSize;
      int index  = 0;
      SolutionSet front = null;
      population.clear();

      // Obtain the next front
      front = ranking.getSubfront(index);

      while ((remain > 0) && (remain >= front.size())){                
        //Assign crowding distance to individuals
        distance.crowdingDistanceAssignment(front, problem_.getNumberOfObjectives());                
        //Add the individuals of this front
        for (int k = 0; k < front.size(); k++ ) {
          population.add(front.get(k));
        } // for

        //Decrement remain
        remain = remain - front.size();

        //Obtain the next front
        index++;
        if (remain > 0) {
          front = ranking.getSubfront(index);
        } // if        
      } // while
      
      // Remain is less than front(index).size, insert only the best one
      if (remain > 0) {  // front contains individuals to insert                        
        distance.crowdingDistanceAssignment(front,problem_.getNumberOfObjectives());
        front.sort(new jmetal.base.operator.comparator.CrowdingComparator());
        for (int k = 0; k < remain; k++) {
          population.add(front.get(k));
        } // for
        
        remain = 0; 
      } // if                               
      
      // This piece of code shows how to use the indicator object into the code
      // of NSGA-II. In particular, it finds the number of evaluations required
      // by the algorithm to obtain a Pareto front with a hypervolume higher
      // than the hypervolume of the true Pareto front.
      if ((indicators != null) && 
          (requiredEvaluations == 0)) {
        double HV = indicators.getHypervolume(population) ;
        if (HV >= (0.98 * indicators.getTrueParetoFrontHypervolume())) {
          requiredEvaluations = evaluations ;
        } // if
      } // if
    } // while
             
    // Return as output parameter the required evaluations
    setOutputParameter("evaluations", requiredEvaluations);
    
    // Return the first non-dominated front
    Ranking ranking = new Ranking(population);        
    return ranking.getSubfront(0);
  } // execute
} // NSGA-II