RouletteWheelSelection.h

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/*!
 *
 *
 * \brief       Implements fitness proportional selection.
 *
 * See http://en.wikipedia.org/wiki/Fitness_proportionate_selection
 *
 *
 *
 * \author      T. Voss
*  \par Copyright (c) 1998-2008:
*      Institut für Neuroinformatik
 * \date        -
 *
 *
 * \par Copyright 1995-2017 Shark Development Team
 *
 * <BR><HR>
 * This file is part of Shark.
 * <http://shark-ml.org/>
 *
 * Shark is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published
 * by the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Shark is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with Shark.  If not, see <http://www.gnu.org/licenses/>.
 *
 */
#ifndef SHARK_ALGORITHMS_DIRECTSEARCH_OPERATORS_SELECTION_ROULETTE_WHEEL_SELECTION_H
#define SHARK_ALGORITHMS_DIRECTSEARCH_OPERATORS_SELECTION_ROULETTE_WHEEL_SELECTION_H

#include <shark/Core/Random.h>
#include <shark/LinAlg/Base.h>

namespace shark {
/**
* \brief Fitness-proportional selection operator.
*
* See http://en.wikipedia.org/wiki/Fitness_proportionate_selection.
*/
struct RouletteWheelSelection {
    /**
    * \brief Selects an individual from the range of individuals with prob. proportional to its fitness.
    * 
    * \param [in] it Iterator pointing to the first valid element.
    * \param [in] itE Iterator pointing to the first invalid element.
    * \param [in] probabilities selection probabilities of the individuals
    */
    template<typename Rng, typename Iterator>
    Iterator operator()(Rng& rng, Iterator it, Iterator itE, RealVector const& probabilities) const
    {
        std::size_t n = probabilities.size();
        double rnd = random::uni(rng, 0,1);
        double sum = 0;
        for(std::size_t pos = 0; pos != n; ++pos,++it){
            sum += probabilities(pos);
            if(rnd <= sum)
                return it;
        }
        return it;
    }
};
}

#endif