//********************************************************
//*Be sure to add headfiles if want to compile this scrpt*
//*This script is developed by iSTEV group1              *
//********************************************************

void homework_1(){

	Double_t mass_sig,ann_sig,mass_bkg,ann_bkg;
	Double_t ann_cut = 0.4;
	Double_t power = 0.;
	Double_t baoliu=0.; 	

	TFile *file = new TFile("tree_group_01.root","r");
	TTree *tr_sig  = (TTree*) file->Get("tree_mc_sig");
	TTree *tr_bck  = (TTree*) file->Get("tree_mc_bkg");

	tr_sig->SetBranchAddress("mass",&mass_sig);
	tr_sig->SetBranchAddress("ann",&ann_sig);

	tr_bck->SetBranchAddress("mass",&mass_bkg);
	tr_bck->SetBranchAddress("ann",&ann_bkg);

	Int_t num_bkg = tr_sig->GetEntriesFast();//data entries 
	Int_t num_sig = tr_bck->GetEntriesFast();
	
	TCanvas* c1 = new TCanvas("c1","c1",900,700);
	gStyle->SetOptStat(0);
	gStyle->SetStatY(0.98);
	gStyle->SetStatX(0.98);
	gStyle->SetStatW(0.3);
	gStyle->SetStatH(0.3);
	c1->SetGridx(1);
	c1->SetGridy(1);
	c1->SetTickx(1);
	c1->SetTicky(1);
	c1->SetFillColor(0);
	c1->SetBorderMode(0);
	c1->SetBorderSize(2);
	c1->SetLeftMargin(0.11);
	c1->SetFrameBorderMode(0);
	c1->SetFrameLineWidth(2);

	TH2F* frame = new TH2F("frame","ann_cut vs S/B;ann_cut;S/B",60,0.3,0.9,550,1.5,20);
	gPad->SetLeftMargin(0.12);
	gPad->SetRightMargin(0.12);
	gPad->SetTopMargin(0.12);
	gPad->SetBottomMargin(0.12);
	gPad->SetFrameLineWidth(0);
	gPad->SetFrameBorderMode(0);
	gPad->SetTickx(1);
	gPad->SetTicky(1);
	gPad->SetLogx(0);
	gPad->SetLogy(0);
	frame->SetLineStyle(1);
	frame->SetLineColor(2);
	frame->SetLineWidth(1);
	frame->GetXaxis()->SetRangeUser(0.3,0.9);
	frame->GetXaxis()->SetTitle("ann_cut");
	frame->GetXaxis()->CenterTitle(false);
	frame->GetXaxis()->SetLabelFont(42);
	frame->GetXaxis()->SetLabelSize(0.05);
	frame->GetXaxis()->SetTitleSize(0.06);
	frame->GetXaxis()->SetTitleOffset(0.9);  
	frame->GetXaxis()->SetNdivisions(8,5,0,kTRUE); 
	frame->GetYaxis()->SetRangeUser(1.5,7);
	frame->GetYaxis()->SetNdivisions(7,9,0,kTRUE);
	frame->GetYaxis()->SetTitle( "S/B" );
	frame->GetYaxis()->CenterTitle(true);
	frame->GetYaxis()->SetLabelFont(42);
	frame->GetYaxis()->SetLabelSize(0.05);
	frame->GetYaxis()->SetTitleSize(0.055);
	frame->GetYaxis()->SetTitleOffset(1.15);
	frame->GetYaxis()->SetNdivisions(8,5,0,kTRUE);
	frame->GetYaxis()->SetTitleFont(42);

	TGraph* g1 = new TGraph(); 

	Double_t total_num_sig=0;//selection events
	Double_t total_num_bkg=0;

	Double_t total_num_bkg_final = total_num_bkg;//bkg number after last cut

	for (Int_t j = 0; j < 1000; j++){
		
		total_num_bkg=0;
		total_num_sig=0;
	
		for(Int_t i = 0; i < num_sig; i++){
			tr_sig -> GetEntry(i);	
			if (ann_sig > ann_cut){
				total_num_sig = total_num_sig+1;
			}
		}

		for(Int_t k = 0; k < num_bkg; k++){
			tr_bck -> GetEntry(k);	
			if (ann_bkg > ann_cut){
				total_num_bkg = total_num_bkg+1;
			}
		}
		
		baoliu = 1-total_num_sig/num_sig;
		if (baoliu >= 0.1)
		{break;}

		power = total_num_sig/total_num_bkg;
		g1->SetPoint(j,ann_cut,power);
		ann_cut = ann_cut + 0.6/1000.;
		total_num_bkg_final = total_num_bkg;
	std::cout<<"***************************************"<<endl;	
	std::cout<<"The ann cut we select is: "<<ann_cut<<endl;
	std::cout<<Form("This cut can reject %f%% background",100.-total_num_bkg_final/num_bkg*100)<<endl;
	}
	
	std::cout<<"The ann cut we select is: "<<ann_cut<<endl;
	std::cout<<Form("This cut can reject %f%% background",100.-total_num_bkg_final/num_bkg*100)<<endl;
	frame->Draw();
	g1->SetLineWidth(2);
	g1->Draw("same");
	c1->Print("ann_cut_effect_0.7732.eps");
	c1->Print("ann_cut_effect_0.7732.bmp");
}