\begin{equation*}
\Sigma_{ij} = \begin{cases}
0.75, & \mbox{if } i\neq j \mbox{ and } i, j \mbox{ are in the same cluster};\\
 1, & \mbox{if } i = j;\\
0.20, & \mbox{otherwise},
 \end{cases}
\end{equation*}
