TCanvas *hstack() {
// Example of stacked histograms: class THStack
//
//  Author: Rene Brun
   
   THStack *hs = new THStack("hs","Stacked 1D histograms");
   //create three 1-d histograms
   TH1F *h1st = new TH1F("h1st","test hstack",100,-4,4);
   h1st->FillRandom("gaus",20000);
   h1st->SetFillColor(kRed);
   h1st->SetMarkerStyle(21);
   h1st->SetMarkerColor(kRed);
   hs->Add(h1st);
   TH1F *h2st = new TH1F("h2st","test hstack",100,-4,4);
   h2st->FillRandom("gaus",15000);
   h2st->SetFillColor(kBlue);
   h2st->SetMarkerStyle(21);
   h2st->SetMarkerColor(kBlue);
   hs->Add(h2st);
   TH1F *h3st = new TH1F("h3st","test hstack",100,-4,4);
   h3st->FillRandom("gaus",10000);
   h3st->SetFillColor(kGreen);
   h3st->SetMarkerStyle(21);
   h3st->SetMarkerColor(kGreen);
   hs->Add(h3st);
   
   TCanvas *cst = new TCanvas("cst","stacked hists",10,10,700,700);
   cst->SetFillColor(41);
   cst->Divide(2,1);
   // in top left pad, draw the stack with defaults
   cst->cd(1);
   hs->Draw();
   // in top right pad, draw the stack with log scale
   // and errors option
   cst->cd(2);
   gPad->SetGrid();
   hs->Draw();
   gPad->SetLogy();

}