def relative_noise_size(self, data, noise):
        '''
        :data: original data as numpy matrix
        :noise: noise matrix as numpy matrix
        '''
        return np.mean([
            sci_dist.cosine(u / la.norm(u), v / la.norm(v))
            for u, v in zip(noise, data)
        ])
:data: original data as numpy matrix
        :noise: noise matrix as numpy matrix