Source code for surrogate.crossover.cxPartialMatch

# Copyright 2016 Quan Pan
# 
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
# 
#    http://www.apache.org/licenses/LICENSE-2.0
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# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
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# limitations under the License.
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# Author: Quan Pan <quanpan302@hotmail.com>
# License: Apache License, Version 2.0
# Create: 2016-12-02

import random

def cxPartialyMatch(var1, var2):
    """Executes a partially matched crossover (PMX) on the input individuals.
    The two individuals are modified in place. This crossover expects
    :term:`sequence` individuals of indices, the result for any other type of
    individuals is unpredictable.

    :param var1: The first variable participating in the crossover.
    :param var2: The second variable participating in the crossover.
    :returns: A tuple of two variables.

    Moreover, this crossover generates two children by matching
    pairs of values in a certain range of the two parents and swapping the values
    of those indexes. For more details see [Goldberg1985]_.

    This function uses the :func:`~random.randint` function from the python base
    :mod:`random` module.

    .. [Goldberg1985] Goldberg and Lingel, "Alleles, loci, and the traveling
       salesman problem", 1985.
    """
    size = min(len(var1), len(var2))
    # size = min(var1.size, var2.size)
    p1, p2 = [0] * size, [0] * size

    # Initialize the position of each indices in the individuals
    for i in xrange(size):
        p1[var1[i]] = i
        p2[var2[i]] = i
    # Choose crossover points
    cxpoint1 = random.randint(0, size)
    cxpoint2 = random.randint(0, size - 1)
    if cxpoint2 >= cxpoint1:
        cxpoint2 += 1
    else:  # Swap the two cx points
        cxpoint1, cxpoint2 = cxpoint2, cxpoint1

    # Apply crossover between cx points
    for i in xrange(cxpoint1, cxpoint2):
        # Keep track of the selected values
        temp1 = var1[i]
        temp2 = var2[i]
        # Swap the matched value
        var1[i], var1[p1[temp2]] = temp2, temp1
        var2[i], var2[p2[temp1]] = temp1, temp2
        # Position bookkeeping
        p1[temp1], p1[temp2] = p1[temp2], p1[temp1]
        p2[temp1], p2[temp2] = p2[temp2], p2[temp1]

    return var1, var2