[gmx-users] bending angle between 2 vectors defined by cm of groups of atoms

[battistia at libero.it]

Dear users and experts,
do you know if it is possible make the bending angle calculation in the following case? 

I have got three groups (G1, G2, G3) into a system.
 I have to define the center of mass of each one. I have to calculate the bending angle defined by vector 1 and vector 2.
vector 1:  by the center of mass of G1 to the center of mass of G2.vector 2:  by the center of mass of G2 to the center of mass of G3

Is it possible do this calculation with gromacs?
Thank you!
Anna