code: def parallactic_angles(self, context):
          
          # Time and antenna extents
          (lt, ut), (la, ua) = context.dim_extents('ntime', 'na')
  
          return (mbu.parallactic_angles(self._times[lt:ut],
                  self._antenna_positions[la:ua], self._phase_dir)
                                              .reshape(context.shape)
                                              .astype(context.dtype))
docs: parallactic angle data source