// Reads the points from a file and produces a simple graph.
int read_graph_txt_MC_data(){
    auto c=new TCanvas();
    c->SetGridy();

    
    // Read MC from txt file TGraphErrors
    TGraphErrors graph1("./mean_variation_MC.txt","%lg %lg %lg %lg");     // * means not select this column of data
   
    graph1.SetTitle("MC;" 
                    "#gamma Energy (GeV);"
                    "#mu of pi0_M_Prefit");
   
    graph1.SetLineWidth(2);
    graph1.SetLineColor(4);
    graph1.SetMarkerStyle(20);
    graph1.SetMarkerColor(kBlue);
    // graph2.SetDrawOption("P");
    // graph1.GetXaxis()->SetRangeUser(0, 2.5); 
    // graph1.GetYaxis()->SetRangeUser(0.13, 0.14); 
    graph1.GetXaxis()->CenterTitle();
    graph1.GetYaxis()->CenterTitle();
    graph1.GetXaxis()->SetTitleSize(0.04);
    graph1.GetYaxis()->SetTitleSize(0.04);
    // graph2.DrawClone("AP");
   

    // Print the data pount
    graph1.Print();
    cout<< "================================================"<< endl;
    
    

    // Read data from txt file TGraphErrors
    TGraphErrors graph2("./mean_variation_data.txt","%lg %lg %lg %lg");     // * means not select this column of data
    graph2.SetTitle("Data;" 
                    "#gamma Energy (GeV);"
                    "#mu of pi0_M_Prefit");
                   
    
    graph2.SetLineWidth(2);
    graph2.SetLineColor(2);
    graph2.SetMarkerStyle(20);
    graph2.SetMarkerColor(kRed);

    // graph1.SetDrawOption("P");
    // graph2.GetXaxis()->SetRangeUser(0, 2.5); 
    // graph2.GetYaxis()->SetRangeUser(0.13, 0.14); 
    graph2.GetXaxis()->CenterTitle();
    graph2.GetYaxis()->CenterTitle();
    graph2.GetXaxis()->SetTitleSize(0.04);
    graph2.GetYaxis()->SetTitleSize(0.04);
    // graph1.DrawClone("AP");
   

    // Print the data pount
    graph2.Print();
    cout<< "================================================"<< endl;

     


    // MultiGraph
    TMultiGraph (mg);
    mg.Add(&graph1);  //, "L"
    mg.Add(&graph2);
    mg.GetXaxis()->SetTitle("#gamma Energy (GeV)");
    mg.GetYaxis()->SetTitle("#sigma of M(#pi^{0})");
    mg.GetXaxis()->CenterTitle();
    mg.GetYaxis()->CenterTitle();
    // mg.GetXaxis()->SetRangeUser(0, 2.5);
    mg.GetHistogram()->GetXaxis()->SetRangeUser(0.,2.5);
    mg.GetYaxis()->SetRangeUser(0.13, 0.14); //mean
    mg.GetXaxis()->SetTitleSize(0.04);
    mg.GetYaxis()->SetTitleSize(0.04);
    mg.GetYaxis()->SetNdivisions(5);
    mg.DrawClone("AP");

    c->Update();
    c->GetFrame()->SetBorderSize(12);
    c->Modified();
    // c->SetLogy();
    // c->SetLogx();
   
    c->BuildLegend();
     return 0;
}