[gmx-users] how to determine the 'afm_dir' vecter and initial spring coordinate 'afm_init'

[zjim]

Hi everyone!
As the manu mentioned, when doing AFM pulling calculation, the spring coordinate is set relative to the reference group in order to start a simulation with zero initial force on the pulled group. but how to know the relative coordinate of the pulled group and how to determine the pull direction and vecter. i can get x, y and z components of distance by 'g_dist', but how can i know the relative  axes of the system.
How do you do to solve such problem,please give me some advice.

thank you in advance!
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