Problem with VMD 'animate' command

From: Chandra Ramananjara (
Date: Sun Feb 12 2006 - 10:12:36 CST

Hi Everyone,
I am having problems using the 'animate' command in VMD and I was wondering if anyone has encountered this problem as well.
I am writing a small & simple Tcl script that steps through the frames of my .dcd trajectory file and prints out the unit cell length of the ensemble in each frame. Something like this:

for { set i $startnum } { $i < $endnum } { incr i $skipnum } {

animate goto $i
set ucl [molinfo top get a]
puts $ucl


The output I get seems to suggest that the 'animate goto' command doesn't actually change the frame.

I experimented a bit and here's what I found out. Starting from scratch, if I load my pdb/dcd file in VMD, and manually set the frame to 0 (using the slide tool on the VMD Main window), then run a simple tcl script (in the VMD TkConsole) to attempt to switch to some random frame, say frame 8:

animate goto 8
puts [molinfo top get frame]

I get 0 as the output, instead of 8. Which means the 'animate goto 8' command in the script I ran doesn't actually change the frame while the program is running. Then if I immediately run another tcl script (trying to switch to some other random frame):

animate goto 22
puts [molinfo top get frame]

I get 8 as the output, instead of 22. This means that the 'animate goto' command only goes into effect after the program finishes running, not while it's running. So the first script I ran (using 'animate goto 8') did work, it just didn't switch to frame 8 until after the program finished running, which isn't very useful. To verify this, I immediately tried the following script:

animate goto 14
puts [molinfo top get frame]

And of course, the output is 22 as expected, not 14.

Any suggestions as to how to get the 'animate' command to switch frames dynamically or on the fly ? This is a really odd bug. Does it have anything to do with the fact that I am compiling/running the script using the VMD TkConsole window provided in the graphics version of VMD ?

Chandra Ramananjara, PhD.

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