[gmx-users] g_wham: How to get the umbrella positions from pullf.xvg when pull-start = no?

[Liping Sunshine]

Dear gmx-users,

I'm doing umbrella samplings using gromacs_4.6.3 after pulling the glucose
through a channel. Here is my pull code:

; Pull code
pull            = umbrella
pull_geometry   = direction
pull-vec1    = 0.0 0.0 -1.0
pull-dim    = N N Y
pull-start      = no
pull_ngroups    = 1
pull_group0    = channel
pull_group1    = glucose
pull_rate1      = 0.0
pull_k1         = 1000
pull-init1      = 0.0

I chose "pull-start = no" because the resulting "umbrella positions" were
totally inversed when I used "pull-start = yes". Therefore, the positions
of each sample is around zero. From what I understood, I can calculate the
"umbrella positions" along "time" from pullf.xvg. Then add the "start
position" to each "umbrella positions" and get the .pdo files like the
following:

# UMBRELLA 3.0
# Component selection: 0 0 1
# nSkip 1
# Ref. Group 'channel'
# Nr. of pull groups 1
# Group 1 'glucose' Umb. Pos. ??? Umb. Cons. 1000.0
#####
0.0000    ???
0.0020    ???
0.0040    ???
0.0060    ???

The problem is how I can calculate the "umbrella positions" along "time"
from pullf.xvg??? Or is there another way to obtain the .pdo files?

Thank you very very much!
sun