I am stuck on how to structure the matrix, can anyone help?

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- Oct 11th 2009, 02:32 PMn7615rLinear Regression Model Matrix
I am stuck on how to structure the matrix, can anyone help?

- Oct 11th 2009, 06:27 PMmatheagle
That's the usual design matrix, X.

The first column is all 1's (n of them)

The second one is x_1 through x_n

Now, when you obtain $\displaystyle X^tX$

you will get a diagonal matrix because the (1,1) position is n.

The (1,2) and (2,1) spot is the sum of the x's which is zero.

And the (2,2) position is $\displaystyle \sum_{i=1}^n x^2_i$