alpha.C

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void alpha()
{

  TGraphErrors  * graph = new TGraphErrors;
  graph->SetName("calibration");

  TH1F *alpha = new TH1F("alpha","",500,-1.0,2.0);
  TH1F *h = new TH1F("h","",200,-1,1);
  TF1 *fT = new TF1("fT","[0]*3/8.*(1+x**2)",-1,1);
  TF1 *fL= new TF1("fL","[0]*3/4.*(1-x**2)",-1,1);
  fT->SetParameter(0,1);
  fL->SetParameter(0,1); 
 
      
  TF1 *f2 = new TF1("f2","[0]*([1]*(3/4)*(1-x**2)+(3/8)*(1-[1])*(1+x**2))",-1,1);
      
  double alphavalue = 0.0;
  int ipoint=0;
  while (alphavalue<=1.0)
    {
      int i = 0;
      alpha->Reset();
            
      for(i = 0; i<1000; i++)
        {
          h->Reset();
          h->FillRandom("fT",floor((1-alphavalue)*10000.));
          h->FillRandom("fL",floor(alphavalue*10000.));
          //h->Draw();
          
          f2->FixParameter(0,h->Integral("bin width"));
          h->Fit("f2","Nq","");
          double alphafit = f2->GetParameter(1);
          alpha->Fill(alphafit);
        }
      
      
      // TCanvas * c3 = new TCanvas("c3","**",800,800);
      //      alpha->Draw();
      double mean = alpha->GetMean(1);
      double rms = alpha->GetRMS(1);
      cout <<"input value of alpha : "<<alphavalue<<endl;
      cout<<"The mean of alpha is: "<<mean<<endl;
      cout<<"The RMS of alpha is: "<<rms<<endl;
      
      double mean_error = rms/sqrt(h->GetEntries());
      cout <<"error on the mean : "<<mean_error<<endl;

      graph->SetPoint(ipoint,alphavalue,mean);
      graph->SetPointError(ipoint++,0,mean_error);

      alphavalue+=0.01;
    }
TCanvas * c3 = new TCanvas("c3","**",800,800);
 graph->Draw("apl"); 


}

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