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diff --git a/src/backend/optimizer/geqo/geqo_px.c b/src/backend/optimizer/geqo/geqo_px.c
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+++ b/src/backend/optimizer/geqo/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 =
+   *  utesch@aut.tu-freiberg.de  * 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"
+
+#if defined(PX)
+
+/* 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++;
+		}
+	}
+}
+
+#endif							/* defined(PX) */