//---------------------------------------------------
//
// combine invariant mass spectra for background @ 8-10 A GeV/c
// into one histogram
//
// Anna Senger a.senger@gsi.de
//
//---------------------------------------------------

void Add_histo(Int_t energy=8, TString type="invM_mix", Int_t NofFiles = 4000)
{
 gStyle->SetCanvasColor(10);
 gStyle->SetFrameFillColor(10);
 gStyle->SetHistLineWidth(6);
 gStyle->SetPadColor(10);
 gStyle->SetStatColor(10);
 gStyle->SetPalette(55);
 
 TString name;

 name.Form("%s_%dgev_0.root",type.Data(),energy);
 TFile *f1 = new TFile(name);
 TH1D *h_bg = ( TH1D *)f1->Get(type.Data());
 TH3D *3Dh_bg = ( TH3D *)f1->Get("YPtM_bg");
 
Double_t N=1;
 
for(int k=1; k<NofFiles+1; k++)
{ 
 name.Form("%s_%dgev_%d.root",type.Data(),energy, k); 
 if(k%100 == 0)
   cout << k << " - " << name << endl;
   
 TFile *f1 = new TFile(name);
 if (!f1 || f1->IsZombie() || f1->GetNkeys() < 1 || f1->TestBit(TFile::kRecovered)){f1->Close(); continue;}
 N++;
 h_bg->Add((TH1D*)f1->Get(type.Data()));
 3Dh_bg->Add((TH3D*)f1->Get("YPtM_bg"));
 
 f1->Close();
}
h_bg->Scale(1./N);
3Dh_bg->Scale(1./N);

 name.Form("%s_%dgev_big.root",type.Data(),energy);
 TFile *FFF = new TFile(name,"recreate");
 h_bg->Write();
 3Dh_bg->Write();
 FFF->Close();
}