/*!
 * 
 *
 * \brief       Simulated binary crossover operator.
 * 
 * 
 *
 * \author      T.Voss
 * \date        2010
 *
 *
 * \par Copyright 1995-2015 Shark Development Team
 * 
 * <BR><HR>
 * This file is part of Shark.
 * <http://image.diku.dk/shark/>
 * 
 * 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_DIRECT_SEARCH_OPERATORS_CROSSOVER_SBX_H
#define SHARK_ALGORITHMS_DIRECT_SEARCH_OPERATORS_CROSSOVER_SBX_H

#include <shark/Rng/GlobalRng.h>
#include <shark/ObjectiveFunctions/BoxConstraintHandler.h>

namespace shark {

        /// \brief Simulated binary crossover operator.
        template<typename PointType>
        struct SimulatedBinaryCrossover {

                SimulatedBinaryCrossover() 
                : m_nc( 20.0 )
                , m_prob( 0.5 ) {}

                /// \brief Initializes the operator for the supplied box-constraints
                void init( RealVector const& lower, RealVector const& upper ) {
                        SIZE_CHECK(lower.size() == upper.size());
                        m_prob = 1./lower.size();
                        m_lower = lower;
                        m_upper = upper;
                }

                /// \brief Mates the supplied individuals.
                /// 
                /// \param [in,out] i1 Individual to be mated.
                /// \param [in,out] i2 Individual to be mated.
                template<class RngType, typename IndividualType>
                void operator()(RngType& rng, IndividualType & i1, IndividualType & i2 )const{  
                        RealVector& point1 = i1.searchPoint();
                        RealVector& point2 = i2.searchPoint();

                        for( unsigned int i = 0; i < point1.size(); i++ ) {

                                if( !coinToss(rng, m_prob ) )
                                        continue;
                                
                                double y1 = 0;
                                double y2 = 0;
                                if( point2[i] < point1[i] ) {
                                        y1 = point2[i];
                                        y2 = point1[i];
                                } else {
                                        y1 = point1[i];
                                        y2 = point2[i];
                                }
                                
                                double betaQ1 = 0.0;
                                double betaQ2 = 0.0;
                                if( std::abs(y2 - y1) < 1E-7 )continue;//equal
                                
                                // Find beta value2
                                double beta1 = 1 + 2 * (y1 - m_lower( i )) / (y2 - y1);
                                double beta2 = 1 + 2 * (m_upper( i ) - y2) / (y2 - y1);
                                double expp = m_nc + 1.;
                                // Find alpha
                                double alpha1 = 2. - std::pow(beta1 , -expp);
                                double alpha2 = 2. - std::pow(beta2 , -expp);

                                double u = uni(rng, 0., 1. );
                                alpha1 *=u;
                                alpha2 *=u;
                                if( u > 1. / alpha1 ) {
                                        alpha1 = 1. / (2. - alpha1);
                                }
                                if( u > 1. / alpha2 ) {
                                        alpha2 = 1. / (2. - alpha2);
                                }
                                betaQ1 = std::pow( alpha1, 1.0/expp );
                                betaQ2 = std::pow( alpha2, 1.0/expp );

                                //recombine points
                                point1[i] = 0.5 * ((y1 + y2) - betaQ1 * (y2 - y1));
                                point2[i] = 0.5 * ((y1 + y2) + betaQ2 * (y2 - y1));
                                // randomly swap loci
                                if( coinToss(rng,0.5) ) std::swap(point1[i], point2[i]);


                                //  -> from Deb's implementation, not contained in any paper
                                point1[i] = std::max( point1[i], m_lower( i ) );
                                point1[i] = std::min( point1[i], m_upper( i ) );
                                point2[i] = std::max( point2[i], m_lower( i ) );
                                point2[i] = std::min( point2[i], m_upper( i ) );
                        }

                }

                /// \brief Serializes this instance to the supplied archive.
                /// \tparam Archive The type of the archive the instance shall be serialized to.
                /// \param [in,out] archive The archive to serialize to.
                /// \param [in] version Version information (optional and not used here).
                double m_nc; ///< Parameter nc.
                double m_prob; ///< Crossover probability.

                RealVector m_upper; ///< Upper bound (box constraint).
                RealVector m_lower; ///< Lower bound (box constraint).
        };
}

#endif

