code: def source_to_neutrino_direction(azimuth, zenith, radian=True):
      
      azimuth = np.atleast_1d(azimuth).copy()
      zenith = np.atleast_1d(zenith).copy()
      if not radian:
          azimuth *= np.pi / 180
          zenith *= np.pi / 180
      phi = (azimuth - np.pi) % (2 * np.pi)
      theta = np.pi - zenith
      if not radian:
          phi *= 180 / np.pi
          theta *= 180 / np.pi
      return phi, theta
docs: Flip the direction.
  
      Parameters
      ==========
      zenith, azimuth: neutrino origin
      radian: bool [default=True]
          receive + return angles in radian? (if false, use degree)