void Ftest(){
  Int_t ndf1=105;
  Int_t ndf2= 102;
  

  TF1 *pdf= new TF1("pdf","TMath::Gamma(([0]+[1])/2)*TMath::Power([0]*x,[0]/2)*TMath::Power([1],[1]/2)/(TMath::Power([0]*x+[1],([0]+[1])/2))",0,5);
  pdf->SetParameters(ndf1,ndf2);
  pdf->SetTitle("F distribution");
  TCanvas *distr= new TCanvas("distr","F test",1000,800);
  pdf->Draw();
 
  Double_t probabilita = pdf->Integral(1,5);        //calcolo probabilità
 
  printf("Probability:%f\n", probabilita);
  




}