docs: def energy_prof(step):
      """Energy flux.
  
      This computation takes sphericity into account if necessary.
  
      Args:
          step (:class:`~stagpy.stagyydata._Step`): a step of a StagyyData
              instance.
      Returns:
          tuple of :class:`numpy.array`: the energy flux and the radial position
          at which it is evaluated.
      """
      diff, rad = diffs_prof(step)
      adv, _ = advts_prof(step)
      return (diff + np.append(adv, 0)), rad