aco/strategy/EASPheromoneStrategy.java

   1 package aco.strategy;
   2
   3 import aco.ant.*;
   4 import aco.mediator.*;
   5
   6 public class EASPheromoneStrategy
   7   extends PheromoneStrategy {
   8
   9   public EASPheromoneStrategy(ACOMediator acom) {
  10     super(acom);
  11   }
  12
  13   public void pheromoneUpdate(Ant[] ants) {
  14     this.evaporate();
  15
  16     for (Ant ant : ants) {
  17       this.depositPheromone(ant);
  18     }
  19
  20     int e = acom.getNumOfCities();
  21     int j = 0, l = 0;
  22
  23     /* enforcement of global best route */
  24     for (int i = 0; i < acom.getNumOfCities(); i++) {
  25       j = acom.getGlobalBestTour(i);
  26       l = acom.getGlobalBestTour(i+1);
  27       acom.setPheromone( j, l, (acom.getPheromone(j,l) +
  28             e/acom.getGlobalBestTourLength()) );
  29     }
  30
  31     acom.computeChoiceInformation();
  32   }
  33
  34   protected void depositPheromone(Ant ant) {
  35     double dt = 1.0/ant.getTourLength();
  36     int j = 0;
  37     int l = 0;
  38     for (int i = 0; i < acom.getNumOfCities(); i++) {
  39       j = ant.getTour(i);
  40       l = ant.getTour(i+1);
  41       /* setPheromone will update j,l and l,j */
  42       acom.setPheromone( j, l, (acom.getPheromone(j,l) + dt) );
  43     }
  44   }
  45
  46   protected void evaporate() {
  47     for (int i = 1; i < acom.getNumOfCities(); i++) {
  48       for (int j = 1; j < acom.getNumOfCities(); j++) {
  49         acom.setPheromone(i, j,
  50             (1.0 - acom.getRoh()) * acom.getPheromone(i, j) );
  51       }
  52     }
  53   }
  54
  55 }