void chi2Draw(double r=1., double x0=0.) {
  gSystem->Load("libMathCore");
  //Double_t r=4.;
  //Double_t x0=0.;

  TCanvas* c1 = new TCanvas("c1", "chi", 100, 10, 700, 700);
  TF1 *pdf1 = new TF1("pdf1", "ROOT::Math::chisquared_pdf(x, [0], [1])",0,13);
  TF1 *pdf2 = new TF1("pdf2", "ROOT::Math::chisquared_pdf(x, [0], [1])",0,13);
  TF1 *pdf3 = new TF1("pdf3", "ROOT::Math::chisquared_pdf(x, [0], [1])",0,13);
  TF1 *pdf4 = new TF1("pdf4", "ROOT::Math::chisquared_pdf(x, [0], [1])",0,13);
  TF1 *pdf8 = new TF1("pdf8", "ROOT::Math::chisquared_pdf(x, [0], [1])",0,13);
  pdf1->SetParameters(r,x0);
  pdf1 -> SetLineColor(kBlack);
  pdf1 -> Draw();
  pdf1->GetYaxis()->SetRangeUser(0.,0.5);
  r+=1;
  pdf2->SetParameters(r,x0);
  pdf2 -> SetLineColor(2);
  pdf2 -> Draw("SAME");
  r+=1;
  pdf3->SetParameters(r,x0);
  pdf3 -> SetLineColor(3);
  pdf3 -> Draw("SAME");
  r+=1;
  pdf4->SetParameters(r,x0);
  pdf4 -> SetLineColor(4);
  pdf4 -> Draw("SAME");
  r=8;
  pdf8->SetParameters(r,x0);
  pdf8 -> SetLineColor(6);
  pdf8 -> Draw("SAME");

  TLegend* tL = new TLegend();
  tL->AddEntry(pdf1,"ndf=1","L");
  tL->AddEntry(pdf2,"ndf=2","L");
  tL->AddEntry(pdf3,"ndf=3","L");
  tL->AddEntry(pdf4,"ndf=4","L");
  tL->AddEntry(pdf8,"ndf=8","L");
  tL->Draw();

  
}