def h(self):
        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.
        """
        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)
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.