\begin{equation}
\label{eq:coeffun}
\beta_j(\mathbf{z}_i)=
\begin{cases}
1-\frac{1}{2r_j}\|\mathbf{z}_i-\mathbf{c}_j\|_2 & \text{if }\|\mathbf{z}_i-\mathbf{c}_j\|_2\leq r_j \\
0 & \text{otherwise}
\end{cases}.
\end{equation}
