docs: def ellplot (mjr, mnr, pa):
      """Utility for debugging."""
      _ellcheck (mjr, mnr, pa)
      import omega as om
  
      th = np.linspace (0, 2 * np.pi, 200)
      x, y = ellpoint (mjr, mnr, pa, th)
      return om.quickXY (x, y, 'mjr=%f mnr=%f pa=%f' %
                         (mjr, mnr, pa * 180 / np.pi))