gr007_multigraph.C

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/// \file
/// \ingroup tutorial_graphs
/// \notebook
/// \preview TMultiGraph is used to combine multiple graphs into one plot. 
/// Allowing to overlay different graphs can be useful for comparing different datasets
/// or for plotting multiple related graphs on the same canvas.
///
/// \macro_image
/// \macro_code
///
/// \author Rene Brun
 
 
void gr007_multigraph() {
   gStyle->SetOptFit();
   auto c1 = new TCanvas("c1","multigraph",700,500);
   c1->SetGrid();
 
   //Initialize a TMultiGraph to hold multiple graphs
   //This ensures the entire dataset from all added graphs is visible without manual range adjustments.
   auto mg = new TMultiGraph();
 
   //Create first graph
   const Int_t n1 = 10;
   Double_t px1[] = {-0.1, 0.05, 0.25, 0.35, 0.5, 0.61,0.7,0.85,0.89,0.95};
   Double_t py1[] = {-1,2.9,5.6,7.4,9,9.6,8.7,6.3,4.5,1};
   Double_t ex1[] = {.05,.1,.07,.07,.04,.05,.06,.07,.08,.05};
   Double_t ey1[] = {.8,.7,.6,.5,.4,.4,.5,.6,.7,.8};
   auto gr1 = new TGraphErrors(n1,px1,py1,ex1,ey1);
   gr1->SetMarkerColor(kBlue);
   gr1->SetMarkerStyle(21);
 
   gr1->Fit("gaus","q");
   auto func1 = (TF1 *) gr1->GetListOfFunctions()->FindObject("gaus");
   func1->SetLineColor(kBlue);
   
   //Add the first graph to the multigraph
   mg->Add(gr1);
 
   //Create second graph
   const Int_t n2 = 10;
   Float_t x2[]  = {-0.28, 0.005, 0.19, 0.29, 0.45, 0.56,0.65,0.80,0.90,1.01};
   Float_t y2[]  = {2.1,3.86,7,9,10,10.55,9.64,7.26,5.42,2};
   Float_t ex2[] = {.04,.12,.08,.06,.05,.04,.07,.06,.08,.04};
   Float_t ey2[] = {.6,.8,.7,.4,.3,.3,.4,.5,.6,.7};
   auto gr2 = new TGraphErrors(n2,x2,y2,ex2,ey2);
   gr2->SetMarkerColor(kRed);
   gr2->SetMarkerStyle(20);
 
   gr2->Fit("pol5","q");
   auto func2 = (TF1 *) gr2->GetListOfFunctions()->FindObject("pol5");
   func2->SetLineColor(kRed);
   func2->SetLineStyle(2);
 
   //Add the second graph to the multigraph
   mg->Add(gr2);
 
   mg->Draw("ap");
 
   //Force drawing of canvas to generate the fit TPaveStats
   c1->Update();
 
   auto stats1 = (TPaveStats*) gr1->GetListOfFunctions()->FindObject("stats");
   auto stats2 = (TPaveStats*) gr2->GetListOfFunctions()->FindObject("stats");
 
   if (stats1 && stats2) {
      stats1->SetTextColor(kBlue);
      stats2->SetTextColor(kRed);
      stats1->SetX1NDC(0.12); stats1->SetX2NDC(0.32); stats1->SetY1NDC(0.82);
      stats2->SetX1NDC(0.72); stats2->SetX2NDC(0.92); stats2->SetY1NDC(0.75);
      c1->Modified();
   }
}