// @(#)root/minuit2:$Id: FumiliFCNBase.h 21530 2007-12-20 11:14:35Z moneta $
// Authors: M. Winkler, F. James, L. Moneta, A. Zsenei   2003-2005  

/**********************************************************************
 *                                                                    *
 * Copyright (c) 2005 LCG ROOT Math team,  CERN/PH-SFT                *
 *                                                                    *
 **********************************************************************/

#ifndef ROOT_Minuit2_FumiliFCNBase
#define ROOT_Minuit2_FumiliFCNBase

#include "Minuit2/FCNBase.h"
#include "Minuit2/ParametricFunction.h"

namespace ROOT {

   namespace Minuit2 {


//____________________________________________________________________________________________
/** 
 
Extension of the FCNBase for the Fumili method. Fumili applies only to 
minimization problems used for fitting. The method is based on a 
linearization of the model function negleting second derivatives. 
User needs to provide the model function. The figure-of-merit describing
the difference between the model function and the actual measurements
has to be implemented by the user in a subclass of FumiliFCNBase.
For an example see the FumiliChi2FCN and FumiliStandardChi2FCN classes.


@author  Andras Zsenei and Lorenzo Moneta, Creation date: 23 Aug 2004

@see <A HREF="http://www.cern.ch/winkler/minuit/tutorial/mntutorial.pdf">MINUIT Tutorial</A> on function minimization, section 5

@see FumiliChi2FCN

@see FumiliStandardChi2FCN

@ingroup Minuit

 */



class FumiliFCNBase : public FCNBase {

public:

   /**
      Default Constructor. Need in this case to create when implementing EvaluateAll the Gradient and Hessian vectors with the right size
   */

   FumiliFCNBase()  : 
      fNumberOfParameters(0), 
      fValue(0)
   {}

   /**

      Constructor which initializes the class with the function provided by the
      user for modeling the data.

      @param npar the number of parameters 

   */


   FumiliFCNBase(unsigned int npar) : 
      fNumberOfParameters(npar),
      fValue(0),
      fGradient(std::vector<double>(npar)), 
      fHessian(std::vector<double>(static_cast<int>( 0.5*npar*(npar+1) )) )            
   {}



//   FumiliFCNBase(const ParametricFunction& modelFCN) { fModelFunction = &modelFCN; }



   virtual ~FumiliFCNBase() {}




   /**
  
      Evaluate function Value, Gradient and Hessian using Fumili approximation, for values of parameters p
      The resul is cached inside and is return from the FumiliFCNBase::Value ,  FumiliFCNBase::Gradient and 
      FumiliFCNBase::Hessian methods 

      @param par vector of parameters

   **/

   virtual  void EvaluateAll( const std::vector<double> & par ) = 0; 


   /**
      Return cached Value of objective function estimated previously using the  FumiliFCNBase::EvaluateAll method

   **/

   virtual double Value() const { return fValue; } 

   /**
      Return cached Value of function Gradient estimated previously using the  FumiliFCNBase::EvaluateAll method
   **/

   virtual const std::vector<double> & Gradient() const { return fGradient; }

   /**
      Return Value of the i-th j-th element of the Hessian matrix estimated previously using the  FumiliFCNBase::EvaluateAll method
      @param row row Index of the matrix
      @param col col Index of the matrix
   **/

   virtual double Hessian(unsigned int row, unsigned int col) const { 
      assert( row < fGradient.size() && col < fGradient.size() ); 
      if(row > col) 
         return fHessian[col+row*(row+1)/2];
      else
         return fHessian[row+col*(col+1)/2];    
   }

   /**
      return number of function variable (parameters) , i.e. function dimension
   */

   virtual unsigned int Dimension() { return fNumberOfParameters; }

protected : 

   /**
      initialize and reset values of gradien and Hessian
   */

   virtual void InitAndReset(unsigned int npar) {
      fNumberOfParameters = npar;
      fGradient = std::vector<double>(npar); 
      fHessian = std::vector<double>(static_cast<int>( 0.5*npar*(npar+1) ));      
   }

   // methods to be used by the derived classes to set the values 
   void SetFCNValue(double Value) { fValue = Value; }

   std::vector<double> & Gradient() { return fGradient; }

   std::vector<double> & Hessian() { return fHessian; }



private:

   // A pointer to the model function which describes the data
   const ParametricFunction *fModelFunction;

   // define these data members protected because can be modified by the derived classes 

private: 

   unsigned int fNumberOfParameters; 
   double fValue; 
   std::vector<double> fGradient; 
   std::vector<double> fHessian;


};

  }  // namespace Minuit2

}  // namespace ROOT

#endif  // ROOT_Minuit2_FumiliFCNBase