Usage: <tt>input = [ <i>ng vx vy vz  gID_1  gID_2  &hellip; gID_ng</i> ] setgroupcomvel</tt>

<p>
Set the center of mass velocity (times <tt>timestep</tt>)
of all groups with ID <tt><i>gID_1, gID_2, &hellip; gID_ng</i></tt>
to <tt><i>vx, vy, vz</i></tt> (in &Aring;).

<p>
Also see <tt>P_com</tt>.

