void quantiles() {

// demo for quantiles

// Authors: Rene Brun, Eddy Offermann

const Int_t nq = 10000;

const Int_t nshots = 10000;

Double_t xq[nq]; // position where to compute the quantiles in [0,1]

Double_t yq[nq]; // array to contain the quantiles

for (Int_t i=0;i<nq;i++) xq[i] = Float_t(i+1)/nq;

TGraph *gr70 = new TGraph(nshots);

TGraph *gr90 = new TGraph(nshots);

TGraph *gr98 = new TGraph(nshots);

TH1F *h = new TH1F("h","demo quantiles",500,-4,4);

for (Int_t shot=0;shot<nshots;shot++) {

h->FillRandom("gaus",50);

h->GetQuantiles(nq,yq,xq);

gr70->SetPoint(shot,shot+1,yq[70]);

gr90->SetPoint(shot,shot+1,yq[90]);

gr98->SetPoint(shot,shot+1,yq[98]);

}

//show the original histogram in the top pad

TCanvas *c1 = new TCanvas("c1","demo quantiles",10,10,600,900);

c1->SetFillColor(41);

c1->Divide(1,3);

c1->cd(1);

h->SetFillColor(38);

h->Draw();

// show the final quantiles in the middle pad

c1->cd(2);

gPad->SetFrameFillColor(33);

gPad->SetGrid();

TGraph *gr = new TGraph(nq,xq,yq);

gr->SetTitle("final quantiles");

gr->SetMarkerStyle(21);

gr->SetMarkerColor(kRed);

gr->SetMarkerSize(0.3);

gr->Draw("ap");

// show the evolution of some quantiles in the bottom pad

c1->cd(3);

gPad->SetFrameFillColor(17);

gPad->DrawFrame(0,0,nshots+1,3.2);

gPad->SetGrid();

gr98->SetMarkerStyle(22);

gr98->SetMarkerColor(kRed);

gr98->Draw("lp");

gr90->SetMarkerStyle(21);

gr90->SetMarkerColor(kBlue);

gr90->Draw("lp");

gr70->SetMarkerStyle(20);

gr70->SetMarkerColor(kMagenta);

gr70->Draw("lp");

// add a legend

TLegend *legend = new TLegend(0.85,0.74,0.95,0.95);

legend->SetTextFont(72);

legend->SetTextSize(0.05);

legend->AddEntry(gr98," q98","lp");

legend->AddEntry(gr90," q90","lp");

legend->AddEntry(gr70," q70","lp");

legend->Draw();

}