using namespace std;
using namespace TMath;

void DrawFitReverse(TGraph *g) {
   TF1* f = g->GetFunction("pol1");
   f->SetBit(TF1::kNotDraw);

   auto gf = new TGraph();
   gf->SetLineColor(kRed);
   gf->SetLineWidth(3);
   int n = 100;
   int np = g->GetN();
   double x1 = g->GetPointX(0);
   double x2 = g->GetPointX(np-1);
   double dx = (x2-x1)/n;
   double x = x1;
   for (int i=0; i<n; i++) {
     gf->SetPoint(i,x,f->Eval(x));
     x = x+dx;
   }
   gf->Draw("L RX");
}

void usccaa(){
   auto in   = new TFile("EfficiencyResults.root");
   auto tree = (TTree*)in->Get("Efficiency");

   double entries, eff, sig1, count, sig2;
   tree->SetBranchAddress("Entries",&entries);
   tree->SetBranchAddress("Efficiency",&eff);
   tree->SetBranchAddress("Eff_Sigma",&sig1);
   tree->SetBranchAddress("Counts",&count);
   tree->SetBranchAddress("Counts_Sigma",&sig2);

   const int ds = tree->GetEntries();

   double hent[ds], hcount[ds], hsig[ds], hex[ds];

   for(int i = 0; i<ds; i++){
      tree->GetEntry(i);
      hent[i] = entries;
      hcount[i] = count;
      hsig[i] = sig2/Sqrt(40);
      hex[i] = 0;
   }

   auto g = new TGraphErrors(ds,hent,hcount,hex,hsig);
   g->Fit("pol1");
   g->GetYaxis()->SetTitle("Counts");
   g->GetXaxis()->SetTitle("Signal");
   g->SetMarkerColor(kBlue);
   g->SetMarkerStyle(20);

   g->Draw("ALP RX");
   DrawFitReverse(g);
}