// [[Rcpp::depends(BH)]]
//===========================================================================
/*!
 * 
 *
 * \brief       A kernel function that wraps a member kernel and multiplies it by a scalar.
 * 
 * 
 *
 * \author      M. Tuma, T. Glasmachers, O. Krause
 * \date        2012
 *
 *
 * \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_MODELS_KERNELS_SCALED_KERNEL_H
#define SHARK_MODELS_KERNELS_SCALED_KERNEL_H


#include <shark/Models/Kernels/AbstractKernelFunction.h>
namespace shark {


/// \brief Scaled version of a kernel function
///
/// For a positive definite kernel k, the scaled kernel
/// \f[ \tilde k(x_1, x_2) := c k(x_1, x_2) \f]
/// is again a positive definite kernel function as long as \f$ c > 0 \f$.
template<class InputType=RealVector>
class ScaledKernel : public AbstractKernelFunction<InputType>
{
private:
        typedef AbstractKernelFunction<InputType> base_type;
public:
        typedef typename base_type::BatchInputType BatchInputType;
        typedef typename base_type::ConstInputReference ConstInputReference;
        typedef typename base_type::ConstBatchInputReference ConstBatchInputReference;

        ScaledKernel( AbstractKernelFunction<InputType>* base, double factor = 1.0 )
        : m_base( base ),
          m_factor( factor )
        {
                RANGE_CHECK( factor > 0 );
                SHARK_ASSERT( base != NULL );
                if ( m_base->hasFirstInputDerivative() ) 
                        this->m_features|=base_type::HAS_FIRST_INPUT_DERIVATIVE;
                if ( m_base->hasFirstParameterDerivative() ) 
                        this->m_features|=base_type::HAS_FIRST_PARAMETER_DERIVATIVE;
        }

        /// \brief From INameable: return the class name.
        std::string name() const
        { return "ScaledKernel"; }

        RealVector parameterVector() const {
                return m_base->parameterVector();
        }
        void setParameterVector(RealVector const& newParameters) {
                m_base->setParameterVector(newParameters);
        }

        std::size_t numberOfParameters() const {
                return m_base->numberOfParameters();
        }
        
        ///\brief creates the internal state of the kernel
        boost::shared_ptr<State> createState()const{
                return m_base->createState();
        }
        
        const double factor() {
                return m_factor;
        }
        void setFactor( double f ) {
                RANGE_CHECK( f > 0 );
                m_factor = f;
        }
        
        const base_type* base() const {
                return m_base;
        }

        double eval(ConstInputReference x1, ConstInputReference x2) const {
                SIZE_CHECK(x1.size() == x2.size());
                return m_factor * m_base->eval(x1, x2);
        }
        
        void eval(ConstBatchInputReference x1, ConstBatchInputReference x2, RealMatrix& result) const{
                m_base->eval(x1, x2,result);
                result *= m_factor;
        }

        void eval(ConstBatchInputReference x1, ConstBatchInputReference x2, RealMatrix& result, State& state) const{
                m_base->eval(x1, x2,result,state);
                result *= m_factor;
        }
        
        /// calculates the weighted derivate w.r.t. the parameters of the base kernel
        void weightedParameterDerivative(
                ConstBatchInputReference batchX1, 
                ConstBatchInputReference batchX2, 
                RealMatrix const& coefficients,
                State const& state, 
                RealVector& gradient
        ) const{
                m_base->weightedParameterDerivative( batchX1, batchX2, coefficients, state, gradient );
                gradient *= m_factor;
        }
        /// calculates the weighted derivate w.r.t. argument \f$ x_1 \f$
        void weightedInputDerivative( 
                ConstBatchInputReference batchX1, 
                ConstBatchInputReference batchX2, 
                RealMatrix const& coefficientsX2,
                State const& state, 
                BatchInputType& gradient
        ) const{
                SIZE_CHECK(coefficientsX2.size1() == shark::size(batchX1));
                SIZE_CHECK(coefficientsX2.size2() == shark::size(batchX2));
                m_base->weightedInputDerivative( batchX1, batchX2, coefficientsX2, state, gradient );
                gradient *= m_factor;
        }
        
        /// \brief The kernel does not serialize anything
        protected:
        AbstractKernelFunction<InputType>* m_base; ///< kernel to scale
        double m_factor; ///< scaling factor
};

typedef ScaledKernel<> DenseScaledKernel;
typedef ScaledKernel<CompressedRealVector> CompressedScaledKernel;
typedef ScaledKernel<ConstRealVectorRange> DenseScaledMklKernel;


}
#endif

