Math 218: Matrices and Vectors

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A=QR Factorizations

We can check if a list of vectors is orthonormal but putting them into the columns of a matrix Q and checking if Q.T*Q == identity_matrix(Q.ncols())

When A=QR, projection onto the column space of A is simplified with P=Q*Q.T.

When A=QR, the least-squares problem [A.T*A | A.T*b] reduces to [R | Q.T*b].