Hi,
I’m a phD student in the university of Strasbourg, France.
First of all, thank you very much for LAMMPS. I’m really enjoying using it.
I have a several question concerning ‘angle style  harmonic’:

Why after calculating the sin (s) you write s=1/s.

I don’t understand the calculation of the forces. Does the matrice ‘a’ represent the dynamical matrice?
how did you calculate it?
 I want to use this harmonic potential but to make a difference between positive and negative angles.
In order to calculate the energy, I thought I can calculate sin(theta) with the vectorial product, and then take
theta=acos© for positive values of sin(theta) and theta=acos(theta) for negative values. But, I don’t know
what to do withe the the functions that calculates the forces? do I need to change them also?
thank you ,
Nava