PoissonLikelihoodFCN.h

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// @(#)root/mathcore:$Id$
// Author: L. Moneta Fri Aug 17 14:29:24 2007

/**********************************************************************
 *                                                                    *
 * Copyright (c) 2007  LCG ROOT Math Team, CERN/PH-SFT                *
 *                                                                    *
 *                                                                    *
 **********************************************************************/

// Header file for class PoissonLikelihoodFCN

#ifndef ROOT_Fit_PoissonLikelihoodFCN
#define ROOT_Fit_PoissonLikelihoodFCN

#ifndef ROOT_Fit_BasicFCN
#include "Fit/BasicFCN.h"
#endif

#ifndef ROOT_Math_IParamFunction
#include "Math/IParamFunction.h"
#endif

#ifndef ROOT_Fit_BinData
#include "Fit/BinData.h"
#endif

#ifndef ROOT_Fit_FitUtil
#include "Fit/FitUtil.h"
#endif


#include <memory>

//#define PARALLEL
// #ifdef PARALLEL
// #ifndef ROOT_Fit_FitUtilParallel
// #include "Fit/FitUtilParallel.h"
// #endif
// #endif

namespace ROOT {

   namespace Fit {


//___________________________________________________________________________________
/**
   class evaluating the log likelihood
   for binned Poisson likelihood fits
   it is template to distinguish gradient and non-gradient case

   @ingroup  FitMethodFunc
*/
template<class FunType>
class PoissonLikelihoodFCN : public BasicFCN<FunType,BinData>  {

public:

   typedef  BasicFCN<FunType,BinData> BaseFCN; 

   typedef  ::ROOT::Math::BasicFitMethodFunction<FunType> BaseObjFunction;
   typedef typename  BaseObjFunction::BaseFunction BaseFunction;

   typedef  ::ROOT::Math::IParamMultiFunction IModelFunction;


   /**
      Constructor from unbin data set and model function (pdf)
   */
   PoissonLikelihoodFCN (const std::shared_ptr<BinData> & data, const std::shared_ptr<IModelFunction> & func, int weight = 0, bool extended = true ) :
      BaseFCN( data, func),
      fIsExtended(extended),
      fWeight(weight),
      fNEffPoints(0),
      fGrad ( std::vector<double> ( func->NPar() ) )
   { }

   /**
      Constructor from unbin data set and model function (pdf) managed by the users
   */
   PoissonLikelihoodFCN (const BinData & data, const IModelFunction & func, int weight = 0, bool extended = true ) :
      BaseFCN(std::shared_ptr<BinData>(const_cast<BinData*>(&data), DummyDeleter<BinData>()), std::shared_ptr<IModelFunction>(dynamic_cast<IModelFunction*>(func.Clone() ) ) ),
      fIsExtended(extended),
      fWeight(weight),
      fNEffPoints(0),
      fGrad ( std::vector<double> ( func.NPar() ) )
   { }


   /**
      Destructor (no operations)
   */
   virtual ~PoissonLikelihoodFCN () {}

   /**
      Copy constructor
   */
   PoissonLikelihoodFCN(const PoissonLikelihoodFCN & f) :
      BaseFCN(f.DataPtr(), f.ModelFunctionPtr() ),
      fIsExtended(f.fIsExtended ),
      fWeight( f.fWeight ),
      fNEffPoints( f.fNEffPoints ),
      fGrad( f.fGrad)
   {  }

   /**
      Assignment operator
   */
   PoissonLikelihoodFCN & operator = (const PoissonLikelihoodFCN & rhs) {
      SetData(rhs.DataPtr() );
      SetModelFunction(rhs.ModelFunctionPtr() );
      fNEffPoints = rhs.fNEffPoints;
      fGrad = rhs.fGrad; 
      fIsExtended = rhs.fIsExtended;
      fWeight = rhs.fWeight; 
   }


   /// clone the function (need to return Base for Windows)
   virtual BaseFunction * Clone() const { return new  PoissonLikelihoodFCN(*this); }

   // effective points used in the fit
   virtual unsigned int NFitPoints() const { return fNEffPoints; }

   /// i-th likelihood element and its gradient
   virtual double DataElement(const double * x, unsigned int i, double * g) const {
      if (i==0) this->UpdateNCalls();
      return FitUtil::EvaluatePoissonBinPdf(BaseFCN::ModelFunction(), BaseFCN::Data(), x, i, g);
   }

   /// evaluate gradient
   virtual void Gradient(const double *x, double *g) const {
      // evaluate the chi2 gradient
      FitUtil::EvaluatePoissonLogLGradient(BaseFCN::ModelFunction(), BaseFCN::Data(), x, g );
   }

   /// get type of fit method function
   virtual  typename BaseObjFunction::Type_t Type() const { return BaseObjFunction::kLogLikelihood; }

   bool IsWeighted() const { return (fWeight != 0); }

   // Use the weights in evaluating the likelihood
   void UseSumOfWeights() {
      if (fWeight == 0) return; // do nothing if it was not weighted
      fWeight = 1;
   }

   // Use sum of the weight squared in evaluating the likelihood
   // (this is needed for calculating the errors)
   void UseSumOfWeightSquare(bool on = true) {
      if (fWeight == 0) return; // do nothing if it was not weighted
      if (on) fWeight = 2;
      else fWeight = 1;
   }


protected:


private:

   /**
      Evaluation of the  function (required by interface)
    */
   virtual double DoEval (const double * x) const {
      this->UpdateNCalls();
      return FitUtil::EvaluatePoissonLogL(BaseFCN::ModelFunction(), BaseFCN::Data(), x, fWeight, fIsExtended, fNEffPoints);
   }

   // for derivatives
   virtual double  DoDerivative(const double * x, unsigned int icoord ) const {
      Gradient(x, &fGrad[0]);
      return fGrad[icoord];
   }


      //data member

   bool fIsExtended; // flag to indicate if is extended (when false is a Multinomial lieklihood), default is true
   int fWeight;  // flag to indicate if needs to evaluate using weight or weight squared (default weight = 0)

   mutable unsigned int fNEffPoints;  // number of effective points used in the fit
   
   mutable std::vector<double> fGrad; // for derivatives

};

      // define useful typedef's
      typedef PoissonLikelihoodFCN<ROOT::Math::IMultiGenFunction> PoissonLLFunction;
      typedef PoissonLikelihoodFCN<ROOT::Math::IMultiGradFunction> PoissonLLGradFunction;


   } // end namespace Fit

} // end namespace ROOT


#endif /* ROOT_Fit_PoissonLikelihoodFCN */