[lammps-users] Question about velocity command

Please see the following command:

“velocity example set NULL NULL 9.0 sum yes units box”

Here, I would like to know the direction of applied velocity. Is it up or down in Z direction(Positive or Negative Z) ?

Besides, if this group of atoms are interacting with other groups of atoms later, how I can trace the instantaneous velocity of this group of atoms? Which commands I should use? Thanks.

9.0 is positive v which is up in z.
You can dump the velocities of atoms via
the dump custom command.