# Hsum¶

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

Author: Rene Brun
This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Tuesday, May 24, 2022 at 03:56 PM.

In [1]:
TCanvas *c1 = new TCanvas("c1","The HSUM example",200,10,600,400);
c1->SetGrid();

gBenchmark->Start("hsum");


Create some histograms.

In [2]:
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

In [3]:
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");

hsum      : Real Time =   0.96 seconds Cpu Time =   0.60 seconds


Draw all canvases

In [4]:
%jsroot on
gROOT->GetListOfCanvases()->Draw()