What does "outputSystemForce" output?

From: Ivan Mikhaylov (ivan.mikhaylov_at_gmail.com)
Date: Wed Jun 05 2013 - 16:28:48 CDT

I defined a colvar "distance" and "forceConstant 10.0" asking for
"oneSiteSystemForce" printing.
I have an output in *.colvars.traj as follows:

# step 1st-colvar fs_1st-colvar
      0 2.70639531217785e+00 0.00000000000000e+00
 1000 2.76803828316001e+00 2.49728670452675e+00
.... ........ ...............
 7000 3.14579942428557e+00 -3.41836799520439e+01

As you see, the very first force is zero and there are positive and
negative values in the third column for the forces.

Equation (50) in section 10.3.1:
does not really help, because it is unclear.

I thought that the force should be equal to distance*forceConstant.
Why is it not?

Could you tell me, please, what "outputSystemForce" outputs?

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