[gmx-users] about the pulling

[Tom]

Dear Gromacs Users or Developers,

I am using the pulling the COM of object A towards B using:
---------------------------------
pull                     = umbrella
pull_geometry            = distance
pull_dim                 = N N Y
pull_start               = yes
pull_ngroups             = 1
pull_group0              = B
pull_group1              = A
pull_rate1               = -0.00005714
pull_k1                  = 5000
-------------------------------
On the output file of pullx.xvg,  the sign of dZ
has been changed from negative to posivitve
or vice vrsa in all sudden. What does it mean?

The following is an example:

@    title "Pull COM"
@    xaxis  label "Time (ps)"
@    yaxis  label "Position (nm)"
@TYPE xy
@ view 0.15, 0.15, 0.75, 0.85
@ legend on
@ legend box on
@ legend loctype view
@ legend 0.78, 0.8
@ legend length 2
@ s0 legend "0 Z"
@ s1 legend "1 dZ"

---------------------------------------------------
173.7400        0.77622 8.14856
173.7500        0.77622 8.14897
173.7600        0.77622 8.14938
173.7700        0.77622 8.14977
173.7800        0.77622 -8.14987
173.7900        0.77622 -8.14954
173.8000        0.77622 -8.14924
173.8100        0.77622 -8.14895
------------------------------------


Thanks a lot for the information!

Thanks,

Tom