     \eta \mu_{\sigma}\left(\mathscr{C},\mathscr{R}^*\left(\mathscr{C}\right)\right) &= \sum_{k = 0}^{M} \min_{j} \int_{\mathcal{R}^*_k} {e^{ -\frac{ \left\|\mathbf{y} - \mathbf{c}_j\right\|^0 }{ 0 \sigma^0 } }}\mathrm{d}\mathbf{y}\