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92 lines
2.7 KiB
C
92 lines
2.7 KiB
C
/*-------------------------------------------------------------------------
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*
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* geqo_selection.c
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* linear selection scheme for the genetic query optimizer
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*
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* Portions Copyright (c) 1996-2004, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/backend/optimizer/geqo/geqo_selection.c,v 1.17 2004/08/29 04:12:33 momjian Exp $
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*
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*-------------------------------------------------------------------------
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*/
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/* contributed by:
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=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
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* Martin Utesch * Institute of Automatic Control *
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= = University of Mining and Technology =
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* utesch@aut.tu-freiberg.de * Freiberg, Germany *
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=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
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*/
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/* this is adopted from D. Whitley's Genitor algorithm */
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/*************************************************************/
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/* */
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/* Copyright (c) 1990 */
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/* Darrell L. Whitley */
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/* Computer Science Department */
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/* Colorado State University */
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/* */
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/* Permission is hereby granted to copy all or any part of */
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/* this program for free distribution. The author's name */
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/* and this copyright notice must be included in any copy. */
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/* */
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/*************************************************************/
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#include "postgres.h"
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#include <math.h>
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#include "optimizer/geqo_copy.h"
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#include "optimizer/geqo_random.h"
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#include "optimizer/geqo_selection.h"
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static int linear(int max, double bias);
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/* geqo_selection
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*
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* according to bias described by input parameters,
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* second genes are selected from the pool
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*/
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void
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geqo_selection(Chromosome *momma, Chromosome *daddy, Pool *pool, double bias)
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{
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int first,
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second;
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first = (int) linear(pool->size, bias);
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second = (int) linear(pool->size, bias);
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if (pool->size > 1)
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{
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while (first == second)
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second = (int) linear(pool->size, bias);
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}
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geqo_copy(momma, &pool->data[first], pool->string_length);
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geqo_copy(daddy, &pool->data[second], pool->string_length);
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}
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/* linear
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* generates random integer between 0 and input max number
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* using input linear bias
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*
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* probability distribution function is: f(x) = bias - 2(bias - 1)x
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* bias = (prob of first rule) / (prob of middle rule)
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*
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*/
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static int
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linear(int pool_size, double bias) /* bias is y-intercept of linear
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* distribution */
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{
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double index; /* index between 0 and pop_size */
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double max = (double) pool_size;
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index = max * (bias - sqrt((bias * bias) - 4.0 * (bias - 1.0) * geqo_rand()))
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/ 2.0 / (bias - 1.0);
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return (int) index;
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}
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