candleplotwhiskers.C

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/// \file
/// \ingroup tutorial_hist
/// \notebook
/// Example of candle plot showing the whiskers definition.
///
/// \macro_image
/// \macro_output
/// \macro_code
///
/// \author Georg Troska
 
void candleplotwhiskers() {
   auto c1 = new TCanvas("c1","Candle Presets",700,800);
   c1->Divide(1,2);
 
   auto rng = new TRandom();
   auto h1 = new TH2I("h1","Gaus",100,-5,5,1,0,1);
   auto h2 = new TH1I("h2","Gaus",100,-5,5);
 
   h1->GetXaxis()->SetTitle("Standard deviation #sigma");
   h2->GetXaxis()->SetTitle("Standard deviation #sigma");
   h2->GetYaxis()->SetTitle("dN/d#sigma");
 
   float myRand;
   for (int i = 0; i < 100000; i++) {
       myRand = rng->Gaus(0,1);
       h1->Fill(myRand,0);
       h2->Fill(myRand);
   }
 
   Double_t *q = new Double_t[3];
   Double_t *p = new Double_t[3];
   q[0] = 0.; q[1] = 0.; q[2] = 0.;
   p[0] = 0.25; p[1] = 0.5; p[2] = 0.75;
 
   h2->GetQuantiles(3,q,p);
   cout << "Q1 (-25%): " << q[0] << " Median: " << q[1] << " Q3 (+25%): " << q[2] << endl;
   double iqr = q[2]-q[0];
   auto mygaus_1_middle = new TF1("mygaus_1_middle","gaus",q[0],q[2]);
   auto mygaus_1_left   = new TF1("mygaus_1_left","gaus",q[0]-1.5*iqr,q[0]);
   mygaus_1_left->SetLineColor(kGreen);
   auto mygaus_1_right  = new TF1("mygaus_1_right","gaus",q[2],q[2]+1.5*iqr);
   mygaus_1_right->SetLineColor(kGreen);
   c1->cd(1);
   h1->SetLineWidth(3);
   h1->SetFillStyle(0);
   h1->Draw("candley2 scat");
 
   c1->cd(2);
   h2->Draw("");
   h2->Fit("mygaus_1_left","R");
   mygaus_1_left->Draw("same");
   auto l3 = new TLine(q[0]-1.5*iqr,0,q[0]-1.5*iqr,mygaus_1_left->Eval(q[0]-1.5*iqr));
   l3->SetLineColor(kGreen); l3->SetLineWidth(2);      l3->Draw("");
   auto l1 = new TLine(q[0]        ,0,q[0]        ,mygaus_1_left->Eval(q[0]));
   l1->SetLineWidth(2);      l1->SetLineColor(kGreen); l1->Draw("");
 
   h2->Fit("mygaus_1_right","R","");
   mygaus_1_right->Draw("same");
   auto l4 = new TLine(q[2]+1.5*iqr,0,q[2]+1.5*iqr,mygaus_1_left->Eval(q[2]+1.5*iqr));
   l4->SetLineColor(kGreen); l4->SetLineWidth(2);      l4->Draw("");
   auto l5 = new TLine(q[2]        ,0,q[2]        ,mygaus_1_right->Eval(q[2]));
   l5->SetLineWidth(2);      l5->SetLineColor(kGreen); l5->Draw("");
 
   h2->Fit("mygaus_1_middle","R");
   mygaus_1_middle->Draw("same");
 
   //In principal one could calculate these values by h2->Integral() as well
   auto t = new TText(); t->SetTextFont(42);
   t->DrawText(0,mygaus_1_middle->Eval(0)/2,"50%");
   t->DrawText(-1.5,mygaus_1_middle->Eval(-1.5)/2,"24.65%");
   t->DrawText(+1,mygaus_1_middle->Eval(+1.5)/2,"24.65%");
   t->DrawText(q[0]-1.5*iqr,1000,Form("%.3f",q[0]-1.5*iqr))->SetTextAngle(90);
   t->DrawText(q[2]+1.5*iqr,1000,Form("%.3f",q[2]+1.5*iqr))->SetTextAngle(90);
   t->DrawText(q[0],1000,Form("%.3f",q[0]))->SetTextAngle(90);
   t->DrawText(q[2],1000,Form("%.3f",q[2]))->SetTextAngle(90);
}