docs: def csep_close(ra, rb):
      """Return the closest separation vector between each point in one set,
      and every point in a second set.
  
      Parameters
      ----------
      ra, rb: float array-like, shape (n, d) and (m, d) in d dimensions.
          Two sets of points. `ra` is the set of points from which the closest
          separation vectors to points `rb` are calculated.
  
      Returns
      -------
      csep_close: float array-like, shape (n, m, d)
          csep[i] is the closest separation vector from point ra[j]
          to any point rb[i].
          Note the un-intuitive vector direction.
      """
      seps = csep(ra, rb)
      seps_sq = np.sum(np.square(seps), axis=-1)
  
      i_close = np.argmin(seps_sq, axis=-1)
  
      i_all = list(range(len(seps)))
      sep = seps[i_all, i_close]
      sep_sq = seps_sq[i_all, i_close]
      return sep, sep_sq