c_eff_linear_fit.C

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#include <TRandom.h>

void GetCCDBConstants(TString path, Int_t run, TString variation, vector<double>& container, Int_t column = 1){
  char command[256];

  sprintf(command, "ccdb dump %s:%i:%s", path.Data(), run, variation.Data());
  FILE* inputPipe = gSystem->OpenPipe(command, "r");
  if(inputPipe == NULL)
    return;
  //get the first (comment) line
  char buff[1024];
  if(fgets(buff, sizeof(buff), inputPipe) == NULL)
    return;
  //get the remaining lines
  double entry;
  int counter = 0;
  while(fgets(buff, sizeof(buff), inputPipe) != NULL){
    istringstream locConstantsStream(buff);
    while (locConstantsStream >> entry){
      counter++;
      if (counter % column == 0) container.push_back(entry);
    }
  }
  //Close the pipe
  gSystem->ClosePipe(inputPipe);
}


// macro that gets TGraphs from the ROOT file generated from the BCAL_point_calibs plugin and returns the effective velocities for each channel, using a quadratic fit
void c_eff_linear_fit(TString fileName = "hd_root.root", int runNumber = 22016, TString variation = "default")
{
        ofstream outfile("c_eff_linear.out");

        //gROOT->Reset();

   // change this to the location and name of your own ROOT file
        TFile *in = new TFile::Open( fileName , "READ");
   if (in == 0) {
     cout << "Unable to open file " << fileName.Data() << "...Exiting" << endl;
     return;
   }

   // histogram to hold the effective velocities
        TH1F* h1_c_eff2 = NULL;

   // function to hold the fit results
        TF1* func2 = NULL;

   // graph for storing the graphs returned from the ROOT file
        TGraph* h2_tgraph = NULL;

        h1_c_eff2 = new TH1F("h1_c_eff2","Effective Velocity per Channel",800,0,800);
        h1_c_eff2->SetXTitle("Channel #");
        h1_c_eff2->SetYTitle("Effective Velocity (cm/ns)");
        h1_c_eff2->GetYaxis()->SetRangeUser(15,19);
        h1_c_eff2->SetMarkerStyle(20);
        h1_c_eff2->SetOption("E1");

        int channels = 768;

   vector<double> effective_velocity;
   GetCCDBConstants("/BCAL/effective_velocities",runNumber, variation, effective_velocity);


        // variables for saving the parameters of the fit
        float eff_velocities_graphs = 0;
        float eff_velocities_graphs_errors = 0;
        float p1_graphs = 0;
        float p1_graphs_error = 0;
        char string[20];

   // loop over the channels, apply a linear fit for each one and calculate the effective velocities
        for(int m = 0; m < channels; ++m){

                sprintf(string,"bcal_point_calibs/h2_tgraph[%d]", m+1);

                h2_tgraph = (TGraph*)in->Get(string);

                if(h2_tgraph->GetN() > 2){
         // linear fit
                        h2_tgraph->Fit("pol1");
                        func2 = h2_tgraph->GetFunction("pol1");
                        p1_graphs = func2->GetParameter(1);
                        p1_graphs_error = func2->GetParError(1);
                        eff_velocities_graphs = effective_velocity[m] / (p1_graphs);
                        eff_velocities_graphs_errors = effective_velocity[m] * p1_graphs_error / ( p1_graphs * p1_graphs );

         outfile << eff_velocities_graphs << endl;
                }

      // fill the histogram
                h1_c_eff2->Fill(m+1,eff_velocities_graphs);
                h1_c_eff2->SetBinError(m+2,eff_velocities_graphs_errors);

      h2_tgraph->Delete();

        } // end of loop over channels

        TCanvas *Canvas_1 = new TCanvas("Canvas_1", "Canvas_1",323,71,953,603);
        Canvas_1->Range(-100,12.25,900,19.75);
        Canvas_1->SetFillColor(0);
        Canvas_1->SetBorderMode(0);
        Canvas_1->SetBorderSize(2);
        Canvas_1->SetFrameBorderMode(0);
        Canvas_1->SetFrameBorderMode(0);


        h1_c_eff2->Draw("");

   // save results
        Canvas_1->SaveAs("h1_c_eff2.png");
        Canvas_1->SaveAs("h1_c_eff2.C");

   in->Close();
   outfile.close();

}