R2Archive.java

//  R2Archive.java
//
//  Author:
//       Antonio J. Nebro <antonio@lcc.uma.es>
//       Juan J. Durillo <juanjo.durillo@gmail.com>
//
//  Copyright (c) 2013 Antonio J. Nebro, Juan J. Durillo
//
//  This program is free software: you can redistribute it and/or modify
//  it under the terms of the GNU Lesser General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  (at your option) any later version.
//
//  This program is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU Lesser General Public License for more details.
// 
//  You should have received a copy of the GNU Lesser General Public License
//  along with this program.  If not, see <http://www.gnu.org/licenses/>.

package jmetal.util.archive;

import jmetal.core.Solution;
import jmetal.qualityIndicator.R2;
import jmetal.util.PseudoRandom;
import jmetal.util.comparators.CrowdingDistanceComparator;
import jmetal.util.comparators.DominanceComparator;
import jmetal.util.comparators.EqualSolutions;

import java.util.Comparator;

/**
 * This class implements a bounded archive based on crowding distances (as
 * defined in NSGA-II).
 */
public class R2Archive extends Archive {
  
  /** 
   * Stores the maximum size of the archive.
   */
  private int maxSize_;
  
  /**
   * stores the number of the objectives.
   */
  private int objectives_;    
  
  /**
   * Stores a <code>Comparator</code> for dominance checking.
   */
  private Comparator dominance_;
  
  /**
   * Stores a <code>Comparator</code> for equality checking (in the objective
   * space).
   */
  private Comparator equals_; 
  
  
  private Comparator crowdingDistance_; 
  
  private R2 r2Indicator_; 

  /**
   * Constructor. Creates an R2Archive for a problem of 2 objectives
   * @param maxSize The maximum size of the archive.
   
   */
  public R2Archive(int maxSize) {
    super(maxSize);
    maxSize_          = maxSize;
    objectives_       = 2;        // hardcoded
    dominance_        = new DominanceComparator();
    equals_           = new EqualSolutions();
    crowdingDistance_ = new CrowdingDistanceComparator();
    r2Indicator_       = new R2();

  } // CrowdingArchive
    
  
  
   /**
   * Constructor. 
   * @param maxSize The maximum size of the archive.
   * @param numberOfObjectives The number of objectives.
   */
  public R2Archive(int maxSize, int numberOfObjectives, String file) {
    super(maxSize);
    maxSize_          = maxSize;
    objectives_       = numberOfObjectives;        
    dominance_        = new DominanceComparator();
    equals_           = new EqualSolutions();
    crowdingDistance_ = new CrowdingDistanceComparator();
    r2Indicator_      = new R2(numberOfObjectives,file);

  } // CrowdingArchive

  
  /**
   * Adds a <code>Solution</code> to the archive. If the <code>Solution</code>
   * is dominated by any member of the archive, then it is discarded. If the 
   * <code>Solution</code> dominates some members of the archive, these are
   * removed. If the archive is full and the <code>Solution</code> has to be
   * inserted, the solutions are sorted by crowding distance and the one having
   * the minimum crowding distance value.
   * @param solution The <code>Solution</code>
   * @return true if the <code>Solution</code> has been inserted, false 
   * otherwise.
   */
  public boolean add(Solution solution){
    int flag = 0;
    int i = 0;
    Solution aux; //Store an solution temporally

    while (i < solutionsList_.size()){
      aux = solutionsList_.get(i);            
            
      flag = dominance_.compare(solution,aux);
      if (flag == 1) {               // The solution to add is dominated
        return false;                // Discard the new solution
      } else if (flag == -1) {       // A solution in the archive is dominated
        solutionsList_.remove(i);    // Remove it from the population            
      } else {
          if (equals_.compare(aux,solution)==0) { // There is an equal solution 
                                                  // in the population
            return false; // Discard the new solution
          }  // if
          i++;
      }
    }
    // Insert the solution into the archive
    solutionsList_.add(solution);        
    if (size() > maxSize_) { // The archive is full
      // Removing the one contributing the less
      int indexWorst = this.r2Indicator_.getWorst(this);
      remove(indexWorst);
    }        
    return true;
  } // add
  
  
  /**
   * Returns a solution from the archive based on their contribution to the R2
   * indicator. The solution is chosen using a binary tournament.   
   */
  public Solution
  getSolution() {
      int index1, index2;
      index1 = PseudoRandom.randInt(0, size()-1);
      index2 = PseudoRandom.randInt(0, size()-1);
      double aux1 = this.r2Indicator_.R2Without(this, index1) ;
      double aux2 = this.r2Indicator_.R2Without(this,index2) ;
      
      if (aux1 > aux2) { // means that index1 contributed less than index2          
          return this.get(index1);
      } else {          
          return this.get(index2);
      }
  }
          
  
  
  
} // R2Archive