[gmx-users] Significance of abscissa in pmf from 2 reactions coordinates

[CROUZY Serge 119222]

Dear Gromacs users

I'm running pull simulations using two reaction coordinates
1) distance between c.o.m. of G1 and G2  (G1 and G2 groups of atoms)
2) distance between c.o.m. of G3 and G2 
same pulling force (umbrella potential), 25 windows 
At the end of the treatment by g_wham I can have 3 profiles
1 corresponding to first distance  (-is option) : G(x1)
2 corresponding to second distance : G(x2)
3 full profile with the two distances : G(xtot??)
The significance of the abscissa in profiles 1 and 2 is clear, but what about in the combined profile (xtot)? 
Since I'm pulling along X only (Fy=Fz=0) I would suggest to correct the xtot given in profile 3 by 0.5(x1+x2).. Is this correct ? 

Thanx for your input
Serge