geqo_ox2.c

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/*------------------------------------------------------------------------
*
* geqo_ox2.c
*
*    order crossover [OX] routines;
*    OX2 operator according to Syswerda
*    (The Genetic Algorithms Handbook, ed L Davis)
*
* src/backend/optimizer/geqo/geqo_ox2.c
*
*-------------------------------------------------------------------------
*/

/* contributed by:
   =*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
   *  Martin Utesch              * Institute of Automatic Control      *
   =                             = University of Mining and Technology =
   *  [email protected]  * Freiberg, Germany                   *
   =*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
 */

/* the ox 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_random.h"
#include "optimizer/geqo_recombination.h"


/* ox2
 *
 *   position crossover
 */
void
ox2(PlannerInfo *root, Gene *tour1, Gene *tour2, Gene *offspring, int num_gene, City *city_table)
{
    int         k,
                j,
                count,
                pos,
                select,
                num_positions;

    /* initialize city table */
    for (k = 1; k <= num_gene; k++)
    {
        city_table[k].used = 0;
        city_table[k - 1].select_list = -1;
    }

    /* determine the number of positions to be inherited from tour1  */
    num_positions = geqo_randint(root, 2 * num_gene / 3, num_gene / 3);

    /* make a list of selected cities */
    for (k = 0; k < num_positions; k++)
    {
        pos = geqo_randint(root, num_gene - 1, 0);
        city_table[pos].select_list = (int) tour1[pos];
        city_table[(int) tour1[pos]].used = 1;  /* mark used */
    }


    count = 0;
    k = 0;

    /* consolidate the select list to adjacent positions */
    while (count < num_positions)
    {
        if (city_table[k].select_list == -1)
        {
            j = k + 1;
            while ((city_table[j].select_list == -1) && (j < num_gene))
                j++;

            city_table[k].select_list = city_table[j].select_list;
            city_table[j].select_list = -1;
            count++;
        }
        else
            count++;
        k++;
    }

    select = 0;

    for (k = 0; k < num_gene; k++)
    {
        if (city_table[(int) tour2[k]].used)
        {
            offspring[k] = (Gene) city_table[select].select_list;
            select++;           /* next city in  the select list   */
        }
        else
            /* city isn't used yet, so inherit from tour2 */
            offspring[k] = tour2[k];
    }

}