SwapMutation.java

//  SwapMutation.java
//
//  Author:
//       Antonio J. Nebro <antonio@lcc.uma.es>
//       Juan J. Durillo <durillo@lcc.uma.es>
//
//  Copyright (c) 2011 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.operators.mutation;

import jmetal.core.Solution;
import jmetal.encodings.solutionType.PermutationSolutionType;
import jmetal.encodings.variable.Permutation;
import jmetal.util.Configuration;
import jmetal.util.JMException;
import jmetal.util.PseudoRandom;

import java.util.Arrays;
import java.util.HashMap;
import java.util.List;

/**
 * This class implements a swap mutation. The solution type of the solution
 * must be Permutation.
 */
public class SwapMutation extends Mutation{
  /**
   * Valid solution types to apply this operator 
   */
  private static final List VALID_TYPES = Arrays.asList(PermutationSolutionType.class) ;
  
  private Double mutationProbability_ = null ;

  /** 
   * Constructor
   */
  public SwapMutation(HashMap<String, Object> parameters) {    
  	super(parameters) ;
  	
  	if (parameters.get("probability") != null)
  		mutationProbability_ = (Double) parameters.get("probability") ;  		
  } // Constructor


  /**
   * Constructor
   */
  //public SwapMutation(Properties properties) {
  //  this();
  //} // 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.getType().getClass() == PermutationSolutionType.class) {

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

	      Class cls = java.lang.String.class;
	      String name = cls.getName(); 
	      throw new JMException("Exception in " + name + ".doMutation()") ;
	    }
  } // 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;
    
		if (!VALID_TYPES.contains(solution.getType().getClass())) {
			Configuration.logger_.severe("SwapMutation.execute: the solution " +
					"is not of the right type. The type should be 'Binary', " +
					"'BinaryReal' or 'Int', but " + solution.getType() + " is obtained");

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

    
    this.doMutation(mutationProbability_, solution);
    return solution;
  } // execute  
} // SwapMutation