code: def h(self):
          r
          if np.size(self._h) > 1:
              assert np.size(self._h) == self.n_modelparams
              return self._h
          else:
              return self._h * np.ones(self.n_modelparams)
docs: r"""
          Returns the step size to be used in numerical differentiation with 
          respect to the model parameters.
          
          The step size is given as a vector with length ``n_modelparams`` so 
          that each model parameter can be weighted independently.