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I'm working on a homework problem, and I'm stuck. I guess my linear algebra still needs some work...

I've arrived at

$\mathbf{D}= \left[ \begin{matrix} \mathbf{C} & \mathbf{1}^T \\ \mathbf{1} & 0 \end{matrix} \right] $

where $\mathbf{C}$ is a $n$ by $n$ matrix and $\mathbf{1}$ is a $n$ by $1$ vector of all ones. I need to find $\mathbf{D}^{-1}$. Can I express it in terms of $\mathbf{C}^{-1}$? Can I proceed at all? Does it help if $\mathbf{C}$ is symmetric?

Thanks

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    @PaulAccisano I think you'll find that you need to permute blocks (at least mentally) so that $\mathbf C$ rather than $0$ comes into the lower-right position of $D$ in the [WP article](http://en.wikipedia.org/wiki/Schur_complement) (with all the mention of Schur complement, I thought at least one link to it would be useful).2012-09-18

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