docs: def params(dirnames, param_func, t_steady=None):
      """Calculate a parameter of a set of model output directories,
      for a measure function which returns an associated uncertainty.
  
      Parameters
      ----------
      dirnames: list[str]
          Model output directory paths.
      param_func: function
          Function which takes a :class:`Model` instance as a single argument,
          and returns the parameter of interest.
  
      Returns
      -------
      params: numpy.ndarray
          Parameters.
      """
      return np.array([param_func(get_recent_model(d)) for d in dirnames])