compute pe/atom angle vs compute angle/local eng theta


I have a question regarding the difference between compute pe/atom angle and compute angle/local eng theta. I know that for compute angle/local eng theta lammps utilizes the dot product to compute the angle and energies between the atom. The index represents the connectivity of the atoms. For example, if I have 3 atoms and the connectivity is 1-2-3 compute angle/local eng theta reports 1 value for the energy and theta while compute pe/atom angle report the angle for 3 atoms. My question is what algorthim does lammps utilizes to compute energy due to angular interaction using compute pe/atom angle.