void calc_2g_yields(){
  double neta[45],dneta[45]; 
  double netap[45],dnetap[45]; 
  for (unsigned int i=1;i<46;i++){
    unsigned int k=i-1;
    double yield[2];
    double unc[2];
    calc_2g_yield(i,yield,unc); 
    neta[k]=yield[0];
    dneta[k]=unc[0];
    netap[k]=yield[1];
    dnetap[k]=unc[1];
  }
  ofstream fout2("eta_2g_yields.dat");
  for (int j=0;j<45;j++){
    fout2 << 2.9+0.2*j << " " << neta[j] << " " << dneta[j] << " " << netap[j] << " " << dnetap[j] 
	  <<endl;
  }
  fout2.close();

  double egamma[45];
  for (int j=0;j<45;j++) egamma[j]=2.9+0.2*j;
  TGraphErrors *g1=new TGraphErrors(45,egamma,neta,0,dneta);
  g1->Draw(); 
  TGraphErrors *g2=new TGraphErrors(45,egamma,netap,0,dnetap);
  g2->Draw("same");



}