geqo_cx.c

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/*------------------------------------------------------------------------
*
* geqo_cx.c
*
*    cycle crossover [CX] routines;
*    CX operator according to Oliver et al
*    (Proc 2nd Int'l Conf on GA's)
*
* src/backend/optimizer/geqo/geqo_cx.c
*
*-------------------------------------------------------------------------
*/

/* contributed by:
   =*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
   *  Martin Utesch              * Institute of Automatic Control      *
   =                             = University of Mining and Technology =
   *  [email protected]  * 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(PlannerInfo *root, 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(root, 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;
}