geqo_recombination.c

来自「PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统」· C语言 代码 · 共 106 行

/*------------------------------------------------------------------------
*
* geqo_recombination.c
*	 misc recombination procedures
*
* $PostgreSQL: pgsql/src/backend/optimizer/geqo/geqo_recombination.c,v 1.15 2005/10/15 02:49:19 momjian Exp $
*
*-------------------------------------------------------------------------
*/

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

/* -- parts of this are adapted from D. Whitley's Genitor algorithm -- */

#include "postgres.h"

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


/*
 * init_tour
 *
 *	 Randomly generates a legal "traveling salesman" tour
 *	 (i.e. where each point is visited only once.)
 *	 Essentially, this routine fills an array with all possible
 *	 points on the tour and randomly chooses the 'next' city from
 *	 this array.  When a city is chosen, the array is shortened
 *	 and the procedure repeated.
 */
void
init_tour(Gene *tour, int num_gene)
{
	Gene	   *tmp;
	int			remainder;
	int			next,
				i;

	/* Fill a temp array with the IDs of all not-yet-visited cities */
	tmp = (Gene *) palloc(num_gene * sizeof(Gene));

	for (i = 0; i < num_gene; i++)
		tmp[i] = (Gene) (i + 1);

	remainder = num_gene - 1;

	for (i = 0; i < num_gene; i++)
	{
		/* choose value between 0 and remainder inclusive */
		next = (int) geqo_randint(remainder, 0);
		/* output that element of the tmp array */
		tour[i] = tmp[next];
		/* and delete it */
		tmp[next] = tmp[remainder];
		remainder--;
	}

	/*
	 * Since geqo_eval() will reject tours where tour[0] > tour[1], we may as
	 * well switch the two to make it a valid tour.
	 */
	if (num_gene >= 2 && tour[0] > tour[1])
	{
		Gene		gtmp = tour[0];

		tour[0] = tour[1];
		tour[1] = gtmp;
	}

	pfree(tmp);
}

/* alloc_city_table
 *
 *	 allocate memory for city table
 */
City *
alloc_city_table(int num_gene)
{
	City	   *city_table;

	/*
	 * palloc one extra location so that nodes numbered 1..n can be indexed
	 * directly; 0 will not be used
	 */
	city_table = (City *) palloc((num_gene + 1) * sizeof(City));

	return city_table;
}

/* free_city_table
 *
 *	  deallocate memory of city table
 */
void
free_city_table(City *city_table)
{
	pfree(city_table);
}