From: Bharat Sharma (
Date: Tue Jun 23 2015 - 11:45:18 CDT

Hello Experts,

I would like to draw the arrow lines on VMD display connecting two atoms. I
follow the following.

proc vmd_draw_arrow {mol start end} {
    # an arrow is made of a cylinder and a cone
    set middle [vecadd $start [vecscale 0.9 [vecsub $end $start]]]
    graphics $mol cylinder $start $middle radius 0.15
    graphics $mol cone $middle $end radius 0.25
vmd_draw_arrow 0 $pos1 $pos2

I need to extend the line to show the angle between two vectors. How do I
do that? One way to do this is finding the coordinate of end point, but how
can I find it?

Any suggestions are appreciated.

Best regards,
Bharat Sharma