geqo_px.c

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

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

/* the px 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"


/* px
 *
 *   position crossover
 */
void
px(PlannerInfo *root, Gene *tour1, Gene *tour2, Gene *offspring, int num_gene,
   City *city_table)
{

    int         num_positions;
    int         i,
                pos,
                tour2_index,
                offspring_index;

    /* initialize city table */
    for (i = 1; i <= num_gene; i++)
        city_table[i].used = 0;

    /* choose random positions that will be inherited directly from parent */
    num_positions = geqo_randint(root, 2 * num_gene / 3, num_gene / 3);

    /* choose random position */
    for (i = 0; i < num_positions; i++)
    {
        pos = geqo_randint(root, num_gene - 1, 0);

        offspring[pos] = tour1[pos];    /* transfer cities to child */
        city_table[(int) tour1[pos]].used = 1;  /* mark city used */
    }

    tour2_index = 0;
    offspring_index = 0;


    /* px main part */

    while (offspring_index < num_gene)
    {

        /* next position in offspring filled */
        if (!city_table[(int) tour1[offspring_index]].used)
        {

            /* next city in tour1 not used */
            if (!city_table[(int) tour2[tour2_index]].used)
            {

                /* inherit from tour1 */
                offspring[offspring_index] = tour2[tour2_index];

                tour2_index++;
                offspring_index++;
            }
            else
            {                   /* next city in tour2 has been used */
                tour2_index++;
            }

        }
        else
        {                       /* next position in offspring is filled */
            offspring_index++;
        }

    }

}