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I have the following equation: $$GCV(\lambda)=\frac{ n\times\text{trace}\{Y'[I-S_{\phi,\lambda}]^{-2}Y\} }{\{\text{trace}[I-S_{\phi,\lambda}]\}^2}$$

I know $I-S_{\phi,\lambda}$ is a matrix what is the power to the -2 supposed to mean? is it the power of each element?

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I would think it's inverse squared. – EuYu Oct 17 '12 at 4:45

I think the natural interpretation of the notation $X^{-2}$ would be the inverse squared.

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