@classmethod
def calculate_energy_loss_function(cls, dielectric):
    """ Calculate energy loss function for a complex spectrum image 
        
        :type  dielectric: np.ndarray
        :param dielectric: the complex dielectric matrix 

        :returns: the energy loss matrix
        """
    return dielectric.imag / (dielectric.real ** 2 + dielectric.imag ** 2)
