// Root macro to plot histogram of q0 and superimpose
// the asymptotic half-chi-square pdf.
// G. Cowan, RHUL Physics, 8 July 2014
// To execute, run root and type .x plot_q0.C at prompt

{

  gROOT->Reset();
  gROOT->LoadMacro("ScaledChi2.C");

  TFile* file = new TFile("inv14.root");
  TH1D* h = (TH1D*)(file->Get("h_q0"));

  TCanvas* c = new TCanvas("c", "c",10,10,500,500);

  c->SetFillColor(0);
  c->SetBorderMode(0);  
  c->SetFrameBorderMode(0);   // need this to turn off red hist frame!
  gROOT->SetStyle("Plain");
  c->UseCurrentStyle();

  gPad->SetLeftMargin(0.17);
  gPad->SetRightMargin(0.05);
  gPad->SetTopMargin(0.07);
  gPad->SetBottomMargin(0.17);

  gStyle->SetOptStat(0);
  gStyle->SetTitleBorderSize(0);
  gStyle->SetTitleSize(0.04);

  gStyle->SetTextFont(42);
  gStyle->SetTextSize(0.04);
  gStyle->SetTitleFont(42, "hxy");    // for histogram and axis title
  gStyle->SetLabelFont(42, "xyz");    // for axis labels (values)

  gStyle->SetTitleOffset(0.8, "h");        // what does this do?
  gStyle->SetTitleX(0.15);
  gStyle->SetTitleY(0.99);

  gROOT->ForceStyle();

  double dx = h->GetBinWidth(1);
  double nExp = h->GetEntries();
  //  double rebinFactor=1;
  //  h->Rebin(rebinFactor);
  //  dx *= rebinFactor;
  double s = 1/(dx*nExp);
  h->Scale(s);

  // move content of underflow bin to bin 1
  double underflow = h->GetBinContent(0);
  double bin1 = h->GetBinContent(1);
  h->SetBinContent(0, 0.);
  h->SetBinContent(1, bin1+underflow);

  h->SetTitle("");
  h->SetXTitle("q_{0}");
  h->SetYTitle("f(q_{0}|0)");

  gPad->SetLogx(0);
  gPad->SetLogy(1);

  TAxis* xa = h->GetXaxis();
  TAxis* ya = h->GetYaxis();

  xa->SetTitleOffset(1.3);    //  factor multiplies default offset
  ya->SetTitleOffset(1.3);

  xa->SetLabelOffset(0.015);
  ya->SetLabelOffset(0.015);

  xa->SetTitleFont(42);
  ya->SetTitleFont(42);

  xa->SetLabelFont(42);
  ya->SetLabelFont(42);

  xa->SetTitleSize(0.05);
  ya->SetTitleSize(0.05);

  xa->SetLabelSize(0.05);
  ya->SetLabelSize(0.05);

  int binLo = h->FindBin(0.);
  int binHi = h->FindBin(30.);
  h->GetXaxis()->SetRange(binLo, binHi);
  h->SetMinimum(5.e-8);
  h->SetMaximum(5.);  
  h->SetLineStyle(1);
  h->SetLineWidth(2);
  h->SetLineColor(kBlack);

  h->Draw();

// Superimpose half chi-square pdf

  double w = 0.5;          // for half-chi-square

  TF1* func = new TF1("func", ScaledChi2, 0., 50., 2);
  func->SetParameter(0,1.0);               // degrees of freedom
  func->SetParameter(1, w);    // scale factor
  func->SetLineStyle(2);
  func->SetLineWidth(2);
  func->SetLineColor(kRed);
  func->Draw("same");

  TLatex* tl = new TLatex();
  tl->SetTextSize(0.04);
  tl->SetTextFont(42);
  tl->SetNDC(true);
  tl->DrawLatex(.46, .85, "n = 12, #tilde{b} = 6.0, #sigma_{#tilde{b}} = 1.0");

  TLegend* leg = new TLegend(0.45, 0.67, .85, .82); // x1, y1, x2, y2
  leg->SetTextSize(0.04);
  leg->SetTextFont(42);
  leg->SetBorderSize(0);
  leg->SetFillColor(0);
  leg->AddEntry(h, "  toy MC", "l");
  leg->AddEntry(func, "  asymptotic formula", "l");
  leg->Draw();

  TPostScript psfile("q0.eps", 113);     // 113 makes eps
  c->Draw();
  psfile.Close();
  c->Print("q0.gif", "gif");

}