[gmx-users] -sel option / g_hbond

[OZGE ENGIN]

Hi, 
 
First of all, thank you very much for your earlier explanations, they helped me much. Now,  I have a  problem with the -sel option of g_hbond. I want to analyze the specific hydrogen bonds in my system, in this respect I created a  file (.ndx), and then I called it with the -sel option. Then, I encountered  the  following error:
 
Invalid command line argument:
-sel

(I use the 3.3.1 version)
 
Should I take the atom numbers from the pdb file in order to represent the atoms in  .ndx file ? 
 
Thank in advance
 
Özge