ARROW

        [GREG2\]ARROW Xref Yref Length Angle [Reference]

    This  command  draws  one or more arrows at given position, and of given
    length, and angle:
      - Xref and Yref define a reference point (in user coordinates) for the
        arrow. The Reference value (5th argument) indicates where this point
        lies on the arrow (0 for the start of the arrow, 0.5 for the  middle
        of the arrow, 1 for the tip of the arrow). Any intermediate value is
        valid; default is 0.5.
      - Length defines the arrow length, in paper units (cm).
      - Angle defines the arrow orientation angle. It is ALWAYS in  DEGREES,
        TRIGONOMETRIC ORIENTATION.
    Additionally, the arrow head size can be customized with SET EXPAND.

    All  the  5  arguments  can be scalar explicit values or scalar variable
    names: this will draw a single arrow. But the 4 first arguments can also
    be  array variables: this will draw as many arrows as the arrays provide
    values (their size have to be consistant). Mixing scalar and array vari-
    able is possible, e.g.
      GREG> ARROW Xarray Yarray 1 AngleArray
    will draw a set of arrows at different positions and orientation angles,
    but all of same length.

    In order to draw arrows defined by a starting point and ending point co-
    ordinates, use commands G\DRAW RELO and G\DRAW ARROW.