A Trick to Improve the Efficiency of Generating Unweighted $B_c$ Events   from BCVEGPY
  In the present paper, we provide an addendum to improve the efficiency of generating unweighted events within PYTHIA environment for the generator BCVEGPY2.1 [C.H. Chang, J.X. Wang and X.G. Wu, Comput.Phys.Commun.{\bf 174}, 241(2006)]. This trick is helpful for experimental simulation. Moreover, the BCVEGPY output has also been improved, i.e. one Les Houches Event common block has been added so as to generate a standard Les Houches Event file that contains the information of the generated $B_c$ meson and the accompanying partons, which can be more conveniently used for further simulation. 
Xian-You Wang and Xing-Gang Wu
hep-ph