// Kompilacja poprzez:
// g++ -o a.out Cstandalone_fitTGraphErrors.C `root-config --cflags --libs`

#include "TF1.h"
#include "TGraphErrors.h"
#include "TMath.h"

#include "TRint.h"       // interfejs do grafiki
#include "TCanvas.h"

using namespace std;

Double_t myFun (Double_t *xarg, Double_t *par) 
{
  Double_t x = xarg[0] , result = 0.; 

  for (int st=0; st<=3; st++) 
    result += par[st] * TMath::Power (x, st);

  return result;
}


int main  (int argc, char * argv[]) 
{
 TRint myRint ("myRint", &argc, argv);
 TCanvas *can1 = new TCanvas ("can1", "can1", 600, 400);

 TGraphErrors gr ("dataPoints.txt");
 gr.SetTitle ();

 TF1 fun ("fun", myFun , -3, 5, 4);
 fun.SetParameters (-1. , 1. , -6. , 1.);
 gr.Fit ( &fun , "" );
 gr.Draw ("AP");
  
 can1->Update();
 cin.ignore();
 return 0;
}