Source code for surrogate.crossover.cxBlend

# 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
# 
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
# Author: Quan Pan <quanpan302@hotmail.com>
# License: Apache License, Version 2.0
# Create: 2016-12-02

import random

def cxBlend(var1, var2, alpha=0.5):
    """Executes a blend crossover that modify in-place the input individuals.
    The blend crossover expects :term:`sequence` individuals of floating point
    numbers.

    :param var1: The first variable participating in the crossover.
    :param var2: The second variable participating in the crossover.
    :param alpha: Extent of the interval in which the new values can be drawn
                  for each attribute on both side of the parents' attributes.
    :returns: A tuple of two variables.

    This function uses the :func:`~random.random` function from the python base
    :mod:`random` module.
    """
    for i, (x1, x2) in enumerate(zip(var1, var2)):
        gamma = (1. + 2. * alpha) * random.random() - alpha
        var1[i] = (1. - gamma) * x1 + gamma * x2
        var2[i] = gamma * x1 + (1. - gamma) * x2

    return var1, var2