void calc_rho_yields(){
  double nrho[45],dnrho[45]; 
  for (unsigned int i=1;i<46;i++){
    unsigned int k=i-1;
    double yield;
    double unc;
    calc_rho_yield(i,yield,unc); 
    nrho[k]=yield;
    dnrho[k]=unc;
  }
  ofstream fout2("rho_yields.dat");
  for (int j=0;j<45;j++){
    fout2 << 2.9+0.2*float(j) << " " << nrho[j] << " " << dnrho[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,nrho,0,dnrho);
  g1->Draw();



}