[help vector]
	[<name>] <Type> [out <filename> [ptrajoutput]] [<mask1>] [<mask2>]
	[magnitude] [ired]
	<Type> = { mask     | minimage  | dipole | center   | corrplane | 
	           box      | boxcenter | ucellx | ucelly   | ucellz    | 
	           momentum | principal [x|y|z]  | velocity | force       }
  Calculate the specified coordinate vector.

    velocity         : Store velocity of atoms in <mask1> (requires velocities).
    force            : Store force of atoms in <mask1> (requires forces).