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 // @(#)root/mathcore:$Id$
 // Author: L. Moneta Mon Nov 13 15:58:13 2006
 
 /**********************************************************************
  *                                                                    *
  * Copyright (c) 2006  LCG ROOT Math Team, CERN/PH-SFT                *
  *                                                                    *
  *                                                                    *
  **********************************************************************/
 
 // Header file for Functor classes.
 // designed is inspired by the Loki Functor
 
 #ifndef ROOT_Math_Functor
 #define ROOT_Math_Functor
 
 #include "Math/IFunction.h"
 
 // #ifndef Root_Math_StaticCheck
 // #include "Math/StaticCheck.h"
 // #endif
 
 #include <algorithm>
 #include <memory>
 #include <functional>
 #include <type_traits>
 #include <vector>
 
 namespace ROOT {
 
 namespace Math {
 
 /**
    Documentation for class Functor class.
    It is used to wrap in a very simple and convenient way multi-dimensional function objects.
    It can wrap all the following types:
    <ul>
    <li> any C++ callable object implementation double operator()( const double *  )
    <li> a free C function of type double ()(const double * )
    <li> an std::function of type std::function<double (double const *)>
    <li> a member function with the correct signature like Foo::Eval(const double * ).
        In this case one pass the object pointer and a pointer to the member function (&Foo::Eval)
    </ul>
    The function dimension is required when constructing the functor.
 
    @ingroup  GenFunc
 
  */
 class Functor : public IBaseFunctionMultiDim  {
 
 public:
 
    /// Default constructor.
    Functor ()  {}
 
    /// Construct from a pointer to member function (multi-dim type).
    template <class PtrObj, typename MemFn>
    Functor(const PtrObj& p, MemFn memFn, unsigned int dim )
       : fDim{dim}, fFunc{std::bind(memFn, p, std::placeholders::_1)}
    {}
 
    /// Construct from a callable object of multi-dimension
    /// with the right signature (implementing `double operator()(const double *x)`).
    Functor(std::function<double(double const *)> const& f, unsigned int dim ) : fDim{dim}, fFunc{f} {}
 
    // clone of the function handler (use copy-ctor)
    Functor * Clone() const override { return new Functor(*this); }
 
    // for multi-dimensional functions
    unsigned int NDim() const override { return fDim; }
 
 private :
 
    inline double DoEval (const double * x) const override {
       return fFunc(x);
    }
 
    unsigned int fDim;
    std::function<double(double const *)> fFunc;
 };
 
 /**
    Functor1D class for one-dimensional functions.
    It is used to wrap in a very simple and convenient way:
    <ul>
    <li> any C++ callable object implementation double operator()( double  )
    <li> a free C function of type double ()(double )
    <li> a member function with the correct signature like Foo::Eval(double ).
        In this case one pass the object pointer and a pointer to the member function (&Foo::Eval)
    </ul>
 
 
    @ingroup  GenFunc
 
  */
 
 class Functor1D : public IBaseFunctionOneDim  {
 
 public:
 
    /// Default constructor.
    Functor1D() = default;
 
    /// Construct from a callable object with the right signature
    /// implementing `double operator() (double x)`.
    Functor1D(std::function<double(double)> const& f) : fFunc{f} {}
 
    // Construct from a pointer to member function (1D type).
    template <class PtrObj, typename MemFn>
    Functor1D(const PtrObj& p, MemFn memFn) : fFunc{std::bind(memFn, p, std::placeholders::_1)} {}
 
    // Clone of the function handler (use copy-ctor).
    Functor1D * Clone() const override { return new Functor1D(*this); }
 
 private :
 
    inline double DoEval (double x) const override {
       return fFunc(x);
    }
 
    std::function<double(double)> fFunc;
 };
 
 /**
    GradFunctor class for Multidimensional gradient functions.
    It is used to wrap in a very C++ callable object to make gradient functions.
    It can be constructed in three different way:
    <ol>
    <li> from an object implementing both
         double operator()( const double * ) for the function evaluation  and
         double Derivative(const double *, int icoord) for the partial derivatives
     <li>from an object implementing any member function like Foo::XXX(const double *) for the function evaluation
         and any member function like Foo::XXX(const double *, int icoord) for the partial derivatives
     <li>from two function objects implementing
         double operator()( const double * ) for the function evaluation and another function object implementing
         double operator() (const double *, int icoord) for the partial derivatives
     <li>from two function objects
    </ol>
    The function dimension is required when constructing the functor.
 
    @ingroup  GenFunc
 
  */
 class GradFunctor : public IGradientFunctionMultiDim  {
 
 
 public:
 
    /// Default constructor.
    GradFunctor() = default;
 
    /**
       construct from a callable object of multi-dimension
       implementing operator()(const double *x) and
       Derivative(const double * x,icoord)
     */
    template <typename Func>
    GradFunctor( const Func & f, unsigned int dim ) :
       fDim{dim}, fFunc{f}, fDerivFunc{std::bind(&Func::Derivative, f, std::placeholders::_1, std::placeholders::_2)}
    {}
 
    /// Construct from a pointer to member function and member function types for function and derivative evaluations.
    template <class PtrObj, typename MemFn, typename DerivMemFn,
              std::enable_if_t<std::is_floating_point<decltype((std::declval<std::remove_pointer_t<PtrObj>>().*
                                                                std::declval<DerivMemFn>())(
                                  std::declval<const double *>(), std::declval<int>()))>::value,
                               bool> = true>
    GradFunctor(const PtrObj &p, MemFn memFn, DerivMemFn gradFn, unsigned int dim)
       : fDim{dim},
         fFunc{std::bind(memFn, p, std::placeholders::_1)},
         fDerivFunc{std::bind(gradFn, p, std::placeholders::_1, std::placeholders::_2)}
    {}
 
    /// Construct from a pointer to member function and member function, types for function and full derivative
    /// evaluations.
    template <
       class PtrObj, typename MemFn, typename GradMemFn,
       std::enable_if_t<std::is_void<decltype((std::declval<std::remove_pointer_t<PtrObj>>().*std::declval<GradMemFn>())(
                           std::declval<const double *>(), std::declval<double *>()))>::value,
                        bool> = true>
    GradFunctor(const PtrObj &p, MemFn memFn, GradMemFn gradFn, unsigned int dim)
       : fDim{dim},
         fFunc{std::bind(memFn, p, std::placeholders::_1)},
         fGradFunc{std::bind(gradFn, p, std::placeholders::_1, std::placeholders::_2)}
    {
    }
 
    /// Construct for Gradient Functions of multi-dimension Func gives the
    /// function evaluation, GradFunc the partial derivatives The function
    /// dimension is required.
    GradFunctor(std::function<double(double const *)> const& f,
                std::function<double(double const *, unsigned int)> const& g, unsigned int dim)
       : fDim{dim}, fFunc{f}, fDerivFunc{g}
    {}
 
    /**
     * @brief Construct a new GradFunctor object using 2 std::function,
     *        one for the function evaluation and one for the Gradient
     *        Note the difference with the constructor above where partial derivative function
     *        is used as input
     *
     * @param f  : function object computing the function value
     * @param dim : number of function dimension
     * @param g   : function object computing the function gradient
     */
    GradFunctor(std::function<double(double const *)> const&f, unsigned int dim,
                std::function<void(double const *, double *)> const& g)
       : fDim{dim}, fFunc{f}, fGradFunc{g}
    {}
 
    // Clone of the function handler (use copy-ctor).
    GradFunctor * Clone() const override { return new GradFunctor(*this); }
 
    // for multi-dimensional functions
    unsigned int NDim() const override { return fDim; }
 
    void Gradient(const double *x, double *g) const override {
       // Fall back to base implementation if no gradient function is provided
       // (it will fill the gradient calling DoDerivative() for each component).
       if(!fGradFunc) {
          IGradientFunctionMultiDim::Gradient(x, g);
          return;
       }
       fGradFunc(x, g);
    }
 
 private :
 
    inline double DoEval (const double * x) const override {
       return fFunc(x);
    }
 
    inline double DoDerivative (const double * x, unsigned int icoord  ) const override {
       if(fDerivFunc) {
          return fDerivFunc(x, icoord);
       }
       // Get the component from the gradient if not derivative function is
       // specified.
       std::vector<double> gradBuffer(fDim);
       std::fill(gradBuffer.begin(), gradBuffer.end(), 0.0);
       fGradFunc(x, gradBuffer.data());
       return gradBuffer[icoord];
    }
 
    unsigned int fDim;
    std::function<double(const double *)> fFunc;
    std::function<double(double const *, unsigned int)> fDerivFunc;
    std::function<void(const double *, double*)> fGradFunc;
 };
 
 
 //_______________________________________________________________________________________________
 /**
    GradFunctor1D class for one-dimensional gradient functions.
    It is used to wrap in a very C++ callable object to make a 1D gradient functions.
    It can be constructed in three different way:
    <ol>
    <li> from an object implementing both
         double operator()( double  ) for the function evaluation  and
         double Derivative(double ) for the partial derivatives
     <li>from an object implementing any member function like Foo::XXX(double ) for the function evaluation
         and any other member function like Foo::YYY(double ) for the derivative.
     <li>from an 2 function objects implementing
         double operator()( double ) . One object provides the function evaluation, the other the derivative.
    </ol>
 
    @ingroup  GenFunc
 
  */
 
 class GradFunctor1D : public IGradientFunctionOneDim  {
 
 public:
 
    /// Default constructor.
    GradFunctor1D() = default;
 
    /// Construct from an object with the right signature,
    /// implementing both `operator() (double x)` and `Derivative(double x)`.
    template <typename Func>
    GradFunctor1D(const Func & f) : fFunc{f}, fDerivFunc{std::bind(&Func::Derivative, f, std::placeholders::_1)} {}
 
    /**
        construct from a pointer to class and two pointers to member functions, one for
        the function evaluation and the other for the derivative.
        The member functions must take a double as argument and return a double
     */
    template <class PtrObj, typename MemFn, typename GradMemFn>
    GradFunctor1D(const PtrObj& p, MemFn memFn, GradMemFn gradFn)
       : fFunc{std::bind(memFn, p, std::placeholders::_1)}, fDerivFunc{std::bind(gradFn, p, std::placeholders::_1)}
    {}
 
 
    /// Specialized constructor from 2 function objects implementing double
    /// operator()(double x). The first one for the function evaluation and the
    /// second one implementing the function derivative.
    GradFunctor1D(std::function<double(double)> const& f, std::function<double(double)> const& g)
       : fFunc{f}, fDerivFunc{g}
    {}
 
    // clone of the function handler (use copy-ctor)
    GradFunctor1D * Clone() const override { return new GradFunctor1D(*this); }
 
 private :
 
    inline double DoEval (double x) const override { return fFunc(x); }
    inline double DoDerivative (double x) const override { return fDerivFunc(x); }
 
    std::function<double(double)> fFunc;
    std::function<double(double)> fDerivFunc;
 };
 
 
 } // end namespace Math
 
 } // end namespace ROOT
 
 
 #endif /* ROOT_Math_Functor */

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