code: def azimuth(v):
      
      v = np.atleast_2d(v)
      azi = phi(v) - np.pi
      azi[azi < 0] += 2 * np.pi
      if len(azi) == 1:
          return azi[0]
      return azi
docs: Return the azimuth angle in radians.
  
      ``phi``, ``theta`` is the opposite of ``zenith``, ``azimuth``.
  
      This is the 'normal' azimuth definition -- beware of how you
      define your coordinates. KM3NeT defines azimuth
      differently than e.g. SLALIB, astropy, the AAS.org