[R] Why H1=1? (H's the hat matrix)

Peng Yu pengyu.ut at gmail.com
Sun Oct 11 20:03:27 CEST 2009

Suppose I have the following hat matrix:

X is a n by p matrix, where n >= p and X_{i,1} = 1

I'm wondering why H1 = 1. (Here, 1 is column vector, whose each
element is the number 1)

Thank you!

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