hsum.C File Reference

Detailed Description

Histograms filled and drawn in a loop.

Simple example illustrating how to use the C++ interpreter to fill histograms in a loop and show the graphics results

void hsum() {
   TCanvas *c1 = new TCanvas("c1","The HSUM example",200,10,600,400);
   c1->SetGrid();

   gBenchmark->Start("hsum");

   // Create some histograms.
   auto total  = new TH1F("total","This is the total distribution",100,-4,4);
   auto main   = new TH1F("main","Main contributor",100,-4,4);
   auto s1     = new TH1F("s1","This is the first signal",100,-4,4);
   auto s2     = new TH1F("s2","This is the second signal",100,-4,4);
   total->Sumw2();  // store the sum of squares of weights
   total->SetMarkerStyle(21);
   total->SetMarkerSize(0.7);
   main->SetFillColor(16);
   s1->SetFillColor(42);
   s2->SetFillColor(46);
   TSlider *slider = 0;

   // Fill histograms randomly
   gRandom->SetSeed();
   const Int_t kUPDATE = 500;
   Float_t xs1, xs2, xmain;
   for ( Int_t i=0; i<10000; i++) {
      xmain = gRandom->Gaus(-1,1.5);
      xs1   = gRandom->Gaus(-0.5,0.5);
      xs2   = gRandom->Landau(1,0.15);
      main->Fill(xmain);
      s1->Fill(xs1,0.3);
      s2->Fill(xs2,0.2);
      total->Fill(xmain);
      total->Fill(xs1,0.3);
      total->Fill(xs2,0.2);
      if (i && (i%kUPDATE) == 0) {
         if (i == kUPDATE) {
            total->Draw("e1p");
            main->Draw("same");
            s1->Draw("same");
            s2->Draw("same");
            c1->Update();
            slider = new TSlider("slider",
               "test",4.2,0,4.6,total->GetMaximum(),38);
            slider->SetFillColor(46);
         }
         if (slider) slider->SetRange(0,Float_t(i)/10000.);
         c1->Modified();
         c1->Update();
      }
   }
   slider->SetRange(0,1);
   total->Draw("sameaxis"); // to redraw axis hidden by the fill area
   c1->Modified();
   gBenchmark->Show("hsum");
}

Author

Rene Brun

Definition in file hsum.C.