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The representation $X=(I_p,0_{n-p\times p})$is confusing me. I get that $I_p$ is an identity matrix with $p$ rows and columns and the rest of the representation is confusing me. Can someone clarify this -simple notation-especially the dimension of $X$?

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More context would definitely help. What book or paper are you seeing this in? Can you post a scan / screenshot of the surrounding text? Can you add examples of how this notation is being used in the source material? – Zev Chonoles Feb 26 '13 at 4:19
The answer in… has this notation. Check it out – qlinck Feb 26 '13 at 4:34
up vote 1 down vote accepted

It's just a typo and should read $(I_p, 0_{p\times(n-p)})$.

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