TChi2ExtendedFCN.cxx

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// @(#)root/minuit2:$Id: TChi2ExtendedFCN.cxx 20880 2007-11-19 11:23:41Z rdm $
// Author: L. Moneta    10/2005  

/**********************************************************************
 *                                                                    *
 * Copyright (c) 2005 ROOT Foundation,  CERN/PH-SFT                   *
 *                                                                    *
 **********************************************************************/

#include "TChi2ExtendedFCN.h"
#include "TChi2ExtendedFitData.h"

#include "TF1.h"
#include "TVirtualFitter.h"
#include <cassert>

//#include <iostream>



TChi2ExtendedFCN::TChi2ExtendedFCN( const TVirtualFitter & fitter) : 
fUp(1.)
{ 
   // constructor : create FitData class and keep a pointer to model function
   fFunc = dynamic_cast<TF1 *> ( fitter.GetUserFunc() );
   assert(fFunc != 0);
   // default skip empty bins
   fData = new TChi2ExtendedFitData(fitter); 
   
   // need to set the size so ROOT can calculate ndf.
   fFunc->SetNumberFitPoints(fData->Size());
}



TChi2ExtendedFCN::~TChi2ExtendedFCN() {  
   //  this class manages the fit data class. Delete it at the end   
   if (fData) { 
      delete fData; 
   }
}


 
double TChi2ExtendedFCN::operator()(const std::vector<double>& par) const {
   // implement chi2 extended function: use also error on x coordinates (can be also asymmetric)  
   
   assert(fData != 0); 
   assert(fFunc != 0); 
   
   
   //  std::cout << "number of params " << par.size() << " in TF1 " << fFunc->GetNpar() << "  " << fFunc->GetNumberFreeParameters() << std::endl;
   
   unsigned int n = fData->Size();
   double chi2 = 0;
   for (unsigned int i = 0; i < n; ++ i) { 
      const std::vector<double> & x = fData->Coords(i); 
      fFunc->InitArgs( &x.front(), &par.front() ); 
      double y = fData->Value(i);
      //std::cout << x[0] << "  " << y << "  " << 1./invError << " params " << par[0] << std::endl;
      double functionValue = fFunc->EvalPar( &x.front(), &par.front() ); 
      
      double ey =  fData->ErrorY(i);
      double exl = fData->ErrorXLow(i);
      double exh = fData->ErrorXUp(i);
      double eux = 0; 
      if (exh <=0 && exl <= 0) 
         eux = 0;
      else 
         // works only for 1D func
         eux = 0.5 * (exl + exh) * fFunc->Derivative( x[0],  const_cast<double *> ( &par.front() ) );
      double error2 = (ey*ey + eux*eux);
      if (error2 == 0) error2 = 1;
      
      double tmp = ( y -functionValue );
                  
      chi2 += tmp*tmp/error2;
   }
   
   return chi2;
}

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