DiffPowers.h

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/*!
 * 
 *
 * \brief       -
 *
 * \author      -
 * \date        -
 *
 *
 * \par Copyright 1995-2017 Shark Development Team
 * 
 * <BR><HR>
 * This file is part of Shark.
 * <https://shark-ml.github.io/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_OBJECTIVEFUNCTIONS_BENCHMARK_DIFFPOWERS_H
#define SHARK_OBJECTIVEFUNCTIONS_BENCHMARK_DIFFPOWERS_H
 
#include <shark/ObjectiveFunctions/AbstractObjectiveFunction.h>
#include <shark/Core/Random.h>
 
 
/// \brief Different powers objective function.
///
/// each dimension is of the form x^a for varying a. This function is ill-conditioned close to the optimum.
/// \ingroup benchmarks
namespace shark {namespace benchmarks{
struct DiffPowers : public SingleObjectiveFunction {
 
    DiffPowers(std::size_t numberOfVariables = 5) {
        m_features |= CAN_PROPOSE_STARTING_POINT;
        m_numberOfVariables = numberOfVariables;
    }
 
    /// \brief From INameable: return the class name.
    std::string name() const
    { return "DiffPowers"; }
 
    std::size_t numberOfVariables()const{
        return m_numberOfVariables;
    }
    
    bool hasScalableDimensionality()const{
        return true;
    }
    
    /// \brief Adjusts the number of variables if the function is scalable.
    /// \param [in] numberOfVariables The new dimension.
    void setNumberOfVariables( std::size_t numberOfVariables ){
        m_numberOfVariables = numberOfVariables;
    }
 
    SearchPointType proposeStartingPoint() const {
        RealVector x(numberOfVariables());
 
        for (std::size_t i = 0; i < x.size(); i++) {
            x(i) = random::uni(*mep_rng, 0,1);
        }
        return x;
    }
 
    double eval( const SearchPointType & p ) const {
        m_evaluationCounter++;
        double sum = 0;
        for( std::size_t i = 0; i < p.size(); i++ ){
            sum += std::pow( std::abs( p( i ) ), 2. + (10.*i) / (p.size() - 1.) );
        }
        return sum;
    }
private:
    std::size_t m_numberOfVariables;
};
}}
 
#endif