void gap_efficiency(void)
{
// 
// plot the number of fits to a cdc segment that result in prob > prob_cut (currently set to 0.01).
//

// #include <TMath.h>
#include <TRandom.h>

gROOT->Reset();
//TTree *Bfield = (TTree *) gROOT->FindObject("Bfield");
gStyle->SetPalette(1,0);
gStyle->SetOptStat(kFALSE);
gStyle->SetOptFit(kFALSE);
// gStyle->SetOptFit(1111);
gStyle->SetPadRightMargin(0.15);
gStyle->SetPadLeftMargin(0.15);
gStyle->SetPadBottomMargin(0.15);
gStyle->SetFillColor(0);
//

   char string[256];
   Int_t j,jj;
   
   #define npts 5;
   #define npts5 2;

   // input data set first point (actually -1) to -10 so that it is not plotted.

   // use offset on x-axis to make data visible and give negative y-values for reference (not plotted)

   Double_t air_gap1[npts]={-1,0.02,0.1,0.2,1};
   Double_t air_gap2[npts]={-1,0.02,0.1,0.2,1};
   Double_t air_gap12[npts]={-1,0.02,0.1,0.2,1};
   Double_t lucite_gap[npts5]={0.02,0.2};

   Double_t air_eff1[npts]={-1,0.598,0.525,0.449,-1};
   Double_t air_eff2[npts]={-1,0.796,0.691,0.557,-1};
   Double_t air_eff12[npts]={-1,0.475,0.366,0.249,-1};
   Double_t lucite_eff[npts5]={0.884,0.871};


   Double_t xmin=0;
   Double_t xmax=0.2;
   Double_t ymin=0;
   Double_t ymax=1;

   //
   TCanvas *c1 = new TCanvas("c1","Efficiency vs gap size",200,10,700,700);
   c1->SetBorderMode(0);
   c1->SetFillColor(0);

   c1->SetGridx();
   c1->SetGridy();
   c1->SetBorderMode(0);
   c1->SetFillColor(0);


   TGraph *air2= new TGraph (npts,air_gap2,air_eff2);
   TGraph *air1= new TGraph (npts,air_gap1,air_eff1);
   TGraph *air12 = new TGraph (npts,air_gap12,air_eff12);
   TGraph *lucite = new TGraph (npts5,lucite_gap,lucite_eff);

   TLegend *leg = new TLegend(0.2,0.20,0.6,0.35);
   leg->AddEntry(lucite,"Lucite Gap1 and Gap2","p");
   leg->AddEntry(air2,"Air Gap2 only","p");
   leg->AddEntry(air1,"Air Gap1 only","p");
   leg->AddEntry(air12,"Air Gap1 and Gap2","p");

   air1->SetTitle("");
   air1->GetXaxis()->SetRangeUser(xmin,xmax);
   air1->GetYaxis()->SetRangeUser(ymin,ymax);
   air1->GetXaxis()->SetTitleSize(0.04);
   air1->GetYaxis()->SetTitleSize(0.04);
   air1->GetYaxis()->SetTitleOffset(1.5);
   air1->GetXaxis()->SetTitle("Gap (cm)");
   air1->GetYaxis()->SetTitle("Efficiency");
   air1->GetXaxis()->SetNdivisions(5);

   air1->SetMarkerColor(2);
   air1->SetMarkerSize(1.5);
   air1->SetMarkerStyle(20);
   air1->Draw("AP");

   air2->SetMarkerColor(4);
   air2->SetMarkerSize(1.5);
   air2->SetMarkerStyle(21);
   air2->Draw("Psame");

   air12->SetMarkerColor(1);
   air12->SetMarkerSize(1.5);
   air12->SetMarkerStyle(22);
   air12->Draw("Psame");

   lucite->SetMarkerColor(1);
   lucite->SetMarkerSize(1.5);
   lucite->SetMarkerStyle(24);
   lucite->Draw("Psame");

   leg->Draw();

   /*air->Fit("pol1","","",0,40);
   TF1 *p1 = air->GetFunction("pol1");
   p1->SetLineColor(1);
   p1->Draw("same");*/

   sprintf(string,"#Lambda rate vs beam current\n");
   t1 = new TLatex(0.45,0.8,string);
   t1->SetTextColor(1);
   t1->SetNDC();
   t1->SetTextSize(0.035);
   // t1->Draw();

   //

   c1->SaveAs("gap_efficiency.eps");
   c1->SaveAs("gap_efficiency.png");

}
Double_t tradeoff (Double_t *x, Double_t *par) {

   Double_t b=par[0];
   Double_t c=par[1];
   Double_t DeE=par[2];
   Double_t E=par[3];
   Double_t x1=x[0]/100;

   char string[256];


   Double_t P = b*b/(DeE*DeE*E);
   Double_t pde = P/2 + sqrt(P*P/4 + x1*c*c/(DeE*DeE*E*E));
   
   /*sprintf (string,"tradeoff=%f b=%f c=%f DeE=%f E=%f\n",pde,b,c,DeE,E);
   printf ("string=%s",string);*/

   return pde;
}