ChiSquareAccumulator.h

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#ifndef LARDATA_UTILITIES_CHISQUAREACCUMULATOR_H
#define LARDATA_UTILITIES_CHISQUAREACCUMULATOR_H


// C/C++ standard libraries
#include <utility> // std::move(), std::forward()


namespace lar {
  namespace util {
    
    template <typename F, typename T = double>
    class ChiSquareAccumulator {
        public:
      using Function_t = F; 
      using Data_t = T; 
      

      ChiSquareAccumulator(Function_t const& expected)
        : fExpected(expected) {}
      // @}
      
      
      // --- BEGIN -- Access to results ----------------------------------------
      
      // @{
      Data_t chiSquare() const { return fChiSq; }
      Data_t operator() () const { return chiSquare(); }
      operator Data_t() const { return chiSquare(); }
      
      unsigned int N() const { return fN; }
      
      Data_t expected(Data_t x) const { return fExpected(x); }
      
      // --- END -- Access to results ------------------------------------------
      
      
      
      // --- BEGIN -- Data manipulation ----------------------------------------
      
      void add(Data_t x, Data_t y)
        { fChiSq += sqr(y - expected(x)); ++fN; }
      
      void add(Data_t x, Data_t y, Data_t s)
        { fChiSq += sqr(z(y, expected(x), s)); ++fN; }
      
      void clear() { fChiSq = Data_t{0}; fN = 0U; }
      
      // --- END -- Data manipulation ------------------------------------------
      
        private:
      unsigned int fN = 0U; 
      Data_t fChiSq = 0.0;  
      
      Function_t fExpected; 
      
      static Data_t z(Data_t x, Data_t mu, Data_t sigma)
        { return (x - mu) / sigma; }
      
      static Data_t sqr(Data_t v) { return v*v; }
      
    }; // ChiSquareAccumulator<>
    
    
    //--------------------------------------------------------------------------
    template <typename F>
    auto makeChiSquareAccumulator(F&& e)
      { return lar::util::ChiSquareAccumulator<F>(std::forward<F>(e)); }

    template <typename T, typename F>
    auto makeChiSquareAccumulator(F&& e)
      { return lar::util::ChiSquareAccumulator<F, T>(std::forward<F>(e)); }
    
    
    //--------------------------------------------------------------------------

  } // namespace util
} // namespace lar



#endif // LARDATA_UTILITIES_CHISQUAREACCUMULATOR_H