void TestMultiGraph()
{
  
  Double_t x1[20] = {1.2, 1.3, 1.4, 1.6, 1.8, 2.3, 2.5, 3, 4, 6, 7, 8, 10,11, 14, 15, 18, 20, 21.3, 22};
  Double_t y1[20] = {2.3, 4.3, 6.3, 30, 80, 150, 500, 2300, 5000, 3020, 600, 120, 80,30, 12, 1, 1e-1, 2e-2, 3.4e-3, 1e-5};
  Double_t ex1[20] = {0.02, 0.02, 0.03, 0.03, 0.05, 0.05, 0.03, 0.02, 0.02, 0.02, 0.01, 0.02, 0.01, 0.04, 0.05, 0.02, 0.02, 0.02, 0.01, 0.01};
  Double_t ey1[20] = {2, 2., 3, 3, 5., 7, 6e2, 2, 3, 2, 1, 2, 1, 4, 5, 2, 2, 2, 2, 1};
  Double_t x2[20], y2[20];
  Double_t x3[20], y3[20];
  
  
  for (Int_t i=0; i<20; i++)
    {
      x2[i] = x1[i]*1.5;
      y2[i] = y1[i]*2.4;
      x3[i] = x1[i]+3.2;
      y3[i] = y1[i] + 5;
      
    }
  
  TGraphErrors *gr1 = new TGraphErrors(20, x1, y1, ex1, ey1);
  TGraphErrors *gr2 = new TGraphErrors(20, x2, y2, ex1, ey1);
  TGraphErrors *gr3 = new TGraphErrors(20, x3, y3, ex1, ey1);
  
  gr1->SetTitle("Graph1");
  gr1->SetMarkerColor(1);
  gr1->SetMarkerStyle(22);
  gr1->SetMarkerSize(1.2);
  
  gr2->SetTitle("Graph2");
  gr2->SetMarkerColor(2);
  gr2->SetMarkerStyle(22);
  gr2->SetMarkerSize(1.2);

  gr3->SetTitle("Graph3");
  gr3->SetMarkerColor(4);
  gr3->SetMarkerStyle(22);
  gr3->SetMarkerSize(1.2);
  
 
  TMultiGraph *mg = new TMultiGraph();
  
  mg->Add(gr1,"PL");
  mg->Add(gr2,"PL");
  mg->Add(gr3,"PL");
  mg->SetTitle("All 3 Graphs");
  
  TCanvas *canvas = new TCanvas("Test of Multigraph");
  canvas->Clear();
  canvas->Divide(2,2);
  canvas->cd(1);
  gPad->SetLogy(1);
  gr1->Draw("APL");
  canvas->cd(2);
  gPad->SetLogy(1);
  gr2->Draw("APL");
  canvas->cd(3);
  gPad->SetLogy(1);
  gr3->Draw("APL");
  canvas->cd(4);
  gPad->SetLogy(1);
  mg->Draw("AP");
  
 
  return; 
}