TeX source:

\hat{V}=\left[\begin{array}{cccc} \hat{V}_{1} & 0 & \cdots & 0 \\ 0 & \hat{V}_{2} & \cdots & 0 \\ \vdots & \vdots & \ddots & \vdots \\ 0 & 0 & \cdots & \hat{V}_{G} \end{array}\right]