geqo_selection.c File Reference

#include "postgres.h"
#include <math.h>
#include "optimizer/geqo_copy.h"
#include "optimizer/geqo_random.h"
#include "optimizer/geqo_selection.h"

Include dependency graph for geqo_selection.c:

Go to the source code of this file.

Functions
static int	linear_rand (PlannerInfo *root, int max, double bias)
void	geqo_selection (PlannerInfo *root, Chromosome *momma, Chromosome *daddy, Pool *pool, double bias)

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Function Documentation

void geqo_selection	(	PlannerInfo *	root,
		Chromosome *	momma,
		Chromosome *	daddy,
		Pool *	pool,
		double	bias
	)

Definition at line 54 of file geqo_selection.c.

References Pool::data, geqo_copy(), linear_rand(), Pool::size, and Pool::string_length.

Referenced by geqo().

{
    int         first,
                second;

    first = linear_rand(root, pool->size, bias);
    second = linear_rand(root, pool->size, bias);

    /*
     * Ensure we have selected different genes, except if pool size is only
     * one, when we can't.
     *
     * This code was observed to hang up in an infinite loop when the
     * platform's implementation of erand48() was broken.  We now always use
     * our own version.
     */
    if (pool->size > 1)
    {
        while (first == second)
            second = linear_rand(root, pool->size, bias);
    }

    geqo_copy(root, momma, &pool->data[first], pool->string_length);
    geqo_copy(root, daddy, &pool->data[second], pool->string_length);
}

static int linear_rand	(	PlannerInfo *	root,
		int	max,
		double	bias
	)			[static]

Definition at line 92 of file geqo_selection.c.

References geqo_rand().

Referenced by geqo_selection().

{
    double      index;          /* index between 0 and pop_size */
    double      max = (double) pool_size;

    /*
     * If geqo_rand() returns exactly 1.0 then we will get exactly max from
     * this equation, whereas we need 0 <= index < max.  Also it seems
     * possible that roundoff error might deliver values slightly outside the
     * range; in particular avoid passing a value slightly less than 0 to
     * sqrt(). If we get a bad value just try again.
     */
    do
    {
        double      sqrtval;

        sqrtval = (bias * bias) - 4.0 * (bias - 1.0) * geqo_rand(root);
        if (sqrtval > 0.0)
            sqrtval = sqrt(sqrtval);
        index = max * (bias - sqrtval) / 2.0 / (bias - 1.0);
    } while (index < 0.0 || index >= max);

    return (int) index;
}