From: Axel Kohlmeyer (
Date: Tue Jun 23 2015 - 12:12:10 CDT

On Tue, Jun 23, 2015 at 12:45 PM, Bharat Sharma
<> wrote:
> 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?

it is not quite clear what you are asking, but it is obvious that the
answer you seek could be found with some simple vector algebra.


> Any suggestions are appreciated.
> Best regards,
> Bharat Sharma

Dr. Axel Kohlmeyer
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.