[gmx-users] plot velocity of center of mass

[Li Qiang]

Dear all users,

I want to plot the velocities of center of mass for my peptide. Reading
from 3.3 manual, there seems to be two ways--g_com and g_traj. 

However,
1, g_com can not be found in /usr/local/gromacs/bin. Is there anything
missed for my installation?

2, $> g_traj -f md.trr -s md.tpr -ov veloc.xvg -com  
but there is only one line in the output file, i.e. the last frame of my
trajectory. The same thing happens for "-of force.xvg". but for "-ox
-coord.xvg" all the times are written out! 
Is there any physical meaning for this? or something is wrong?

GROMACS 3.3.1 is used.

thank you

Qiang