#include "TGraphErrors.h"
#include "TCanvas.h"


void Exercise6b()
{

  //  const int kN = 100;
  const int kN = 4;

  Double_t x[4] = {34.5,45.0,65.3,80.5};
  Double_t y[4] = {2071., 2098., 2147., 2164.};

  Double_t errx[4] = {0.1, 0.1, 0.1, 0.1};
  Double_t erry[4] = {3.,2.,3.,4.};

  TGraphErrors* gra[2];
  for(int i = 0; i < 2; i++){
    gra[i] = new TGraphErrors(kN);
  } // crete 2 tgraph
  
  

  for(int i = 0; i < kN; i++){
    gra[0]->SetPoint(i, x[i], y[i]);
    gra[1]->SetPoint(i, y[i], x[i]); // change x<=>y
    gra[0]->SetPointError(i, errx[i], erry[i]);
    gra[1]->SetPointError(i, erry[i], errx[i]); // change ex<=>ey
  } // i
  
  
  
  
  TCanvas* can = new TCanvas("can", "can");
  can->Divide(2, 1);

  for(int i = 0; i < 2; i++){
    can->cd(i + 1);
    gra[i]->Draw("ap");
    gra[i]->Fit("pol1");
  } // i

  
  //  Way 2 

  TGraphErrors* gra1[2];
  
  gra1[0] = new TGraphErrors(kN,x,y,errx,erry);
  gra1[1] = new TGraphErrors(kN,x,y,erry,errx);

  gra1[0]->SetTitle("Original Errors");
  gra1[1]->SetTitle("Swap errors");

  
  TCanvas* can1 = new TCanvas("can1", "can1");
  can1->Divide(2, 1);
  for(int i = 0; i < 2; i++){
    can1->cd(i + 1);
    gra1[i]->Draw("ap");
    gra1[i]->Fit("pol1");
  } // i

}