swapmutation.java

这是多目标进化算法包

/**
 * SwapMutation.java
 * Class representing a swap mutation operator
 * @author Antonio J.Nebro
 * @version 1.0
 */

package jmetal.base.operator.mutation;

import jmetal.base.Configuration;
import jmetal.base.Solution;
import jmetal.base.variable.*;
import jmetal.util.JMException;
import jmetal.util.PseudoRandom;
import jmetal.base.Operator;
import jmetal.base.Configuration.VariableType_; 

/**
 * This class implements a swap mutation.
 * NOTE: the operator is applied to the first variable of the solutions, and 
 * the type of those variables must be <code>VariableType_.Permutation</code>.
 */
public class SwapMutation extends Operator{
  /** 
   * Constructor
   */
  public SwapMutation() {    
  } // Constructor
  
  /**
   * Performs the operation
   * @param probability Mutation probability
   * @param solution The solution to mutate
   * @throws JMException 
   */
  public void doMutation(double probability, Solution solution) throws JMException {   
    int permutation[] ;
    int permutationLength ;
    if (solution.getDecisionVariables().variables_[0].getVariableType() ==
      VariableType_.Permutation) {

      permutationLength = ((Permutation)solution.getDecisionVariables().variables_[0]).getLength() ;
      permutation = ((Permutation)solution.getDecisionVariables().variables_[0]).vector_ ;

      if (PseudoRandom.randDouble() < probability) {
        int pos1 ;
        int pos2 ;

        pos1 = PseudoRandom.randInt(0,permutationLength-1) ;
        pos2 = PseudoRandom.randInt(0,permutationLength-1) ;

        while (pos1 == pos2) {
          if (pos1 == (permutationLength - 1)) 
            pos2 = PseudoRandom.randInt(0, permutationLength- 2);
          else 
            pos2 = PseudoRandom.randInt(pos1, permutationLength- 1);
        } // while
        // swap
        int temp = permutation[pos1];
        permutation[pos1] = permutation[pos2];
        permutation[pos2] = temp;    
      } // if
    } // if
    else  {
      Configuration.logger_.severe("SwapMutation.doMutation: invalid type. " +
          ""+ solution.getDecisionVariables().variables_[0].getVariableType());

      Class cls = java.lang.String.class;
      String name = cls.getName(); 
      throw new JMException("Exception in " + name + ".doMutation()") ;
    } // catch               
  } // doMutation

  /**
   * Executes the operation
   * @param object An object containing the solution to mutate
   * @return an object containing the mutated solution
   * @throws JMException 
   */
  public Object execute(Object object) throws JMException {
    Solution solution = (Solution)object;

    Double probability = (Double)getParameter("probability");       
    if (probability == null)
    {
      Configuration.logger_.severe("SwapMutation.execute: probability " +
      "not specified");
      Class cls = java.lang.String.class;
      String name = cls.getName(); 
      throw new JMException("Exception in " + name + ".execute()") ;  
    }
    
    this.doMutation(probability.doubleValue(), solution);
    return solution;
  } // execute  
} // SwapMutation