Calculate the psi torsions of a trajectory.
traj : Trajectory
Trajectory for which you want dihedrals.
opt : bool, default=True
Use an optimized native library to calculate angles.
indices : np.ndarray, shape=(n_psi, 4)
The indices of the atoms involved in each of the psi dihedral angles
angles : np.ndarray, shape=(n_frames, n_psi)
The value of the dihedral angle for each of the angles in each of the frames.