#include "Fit/BinData.h"
#include "Fit/Fitter.h"
#include "Math/WrappedMultiTF1.h"
#include "TF1.h"
#include "TRandom.h"

using namespace ROOT::Fit; 
using namespace ROOT::Math; 

void fitArray() { 

   // generate first data arrays
   const int n = 100; 
   double x[n]; 
   double y[n]; 
   double erry[n]; // error in y

   double A = 2; 
   double B = 3; 
   double E = 0.1; 
   for (int i = 0; i < n; ++i) { 
      x[i] = static_cast<double> (i); 
      // generate y as a linear funxtion of x plus a random gaussian term 
      y[i] = A * x[i] + B + gRandom->Gaus(0, E); 
      erry[i] = E; 
   }

   // now fit the data
   TF1 * f1 = new TF1("f1","pol1"); 
   
   // create fit data class 
   double *errx = 0; //assume no error in x
   ROOT::Fit::BinData data(n,x,y, errx, erry); 
   // create function class 
   ROOT::Math::WrappedMultiTF1 wf(*f1); 
   // create fitter class and fit
   ROOT::Fit::Fitter fitter; 
   if (!fitter.Fit(data, wf) ) 
      std::cerr << "Error Fitting " << std::endl;
   else 
      fitter.Result().Print(std::cout);


}