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geqo_cx.c

/*------------------------------------------------------------------------
*
* geqo_cx.c
*
*      cycle crossover [CX] routines;
*      CX operator according to Oliver et al
*      (Proc 2nd Int'l Conf on GA's)
*
* $PostgreSQL: pgsql/src/backend/optimizer/geqo/geqo_cx.c,v 1.10 2003/11/29 22:39:49 pgsql Exp $
*
*-------------------------------------------------------------------------
*/

/* contributed by:
   =*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
   *  Martin Utesch                        * Institute of Automatic Control      *
   =                                       = University of Mining and Technology =
   *  utesch@aut.tu-freiberg.de  * Freiberg, Germany                       *
   =*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
 */

/* the cx algorithm is adopted from Genitor : */
/*************************************************************/
/*                                                                                         */
/*    Copyright (c) 1990                                                             */
/*    Darrell L. Whitley                                                             */
/*    Computer Science Department                                              */
/*    Colorado State University                                                */
/*                                                                                         */
/*    Permission is hereby granted to copy all or any part of  */
/*    this program for free distribution.   The author's name  */
/*    and this copyright notice must be included in any copy.  */
/*                                                                                         */
/*************************************************************/


#include "postgres.h"
#include "optimizer/geqo_recombination.h"
#include "optimizer/geqo_random.h"


/* cx
 *
 *     cycle crossover
 */
int
cx(Gene *tour1, Gene *tour2, Gene *offspring, int num_gene, City *city_table)
{

      int               i,
                        start_pos,
                        curr_pos;
      int               count = 0;
      int               num_diffs = 0;

      /* initialize city table */
      for (i = 1; i <= num_gene; i++)
      {
            city_table[i].used = 0;
            city_table[tour2[i - 1]].tour2_position = i - 1;
            city_table[tour1[i - 1]].tour1_position = i - 1;
      }

      /* choose random cycle starting position */
      start_pos = geqo_randint(num_gene - 1, 0);

      /* child inherits first city  */
      offspring[start_pos] = tour1[start_pos];

      /* begin cycle with tour1 */
      curr_pos = start_pos;
      city_table[(int) tour1[start_pos]].used = 1;

      count++;

      /* cx main part */


/* STEP 1 */

      while (tour2[curr_pos] != tour1[start_pos])
      {
            city_table[(int) tour2[curr_pos]].used = 1;
            curr_pos = city_table[(int) tour2[curr_pos]].tour1_position;
            offspring[curr_pos] = tour1[curr_pos];
            count++;
      }


/* STEP 2 */

      /* failed to create a complete tour */
      if (count < num_gene)
      {
            for (i = 1; i <= num_gene; i++)
            {
                  if (!city_table[i].used)
                  {
                        offspring[city_table[i].tour2_position] =
                              tour2[(int) city_table[i].tour2_position];
                        count++;
                  }
            }
      }


/* STEP 3 */

      /* still failed to create a complete tour */
      if (count < num_gene)
      {

            /* count the number of differences between mom and offspring */
            for (i = 0; i < num_gene; i++)
                  if (tour1[i] != offspring[i])
                        num_diffs++;

      }

      return num_diffs;
}

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