Exercise 2179Linear algebra › Matrices and linear systemsL1Added 3 Nov 2026
QR factorization by Gram-Schmidt
#QR factorization#Gram-Schmidt#orthogonalization
Statement
Find the QR factorization of A=110101.
Hint
Apply Gram-Schmidt to the columns of A.
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Solution
Columns.a1=(1,1,0), a2=(1,0,1).
First vector.q1=a1/∥a1∥=(1,1,0)/2.
Projection.⟨a2,q1⟩=(1⋅1+0⋅1+1⋅0)/2=1/2. The orthogonal part is a2−⟨a2,q1⟩q1=(1,0,1)−21(1,1,0)=(1/2,−1/2,1). Normalize: ∥a2−⟨a2,q1⟩q1∥=1/4+1/4+1=3/2. So q2=2/3(1/2,−1/2,1)=(1/6,−1/6,2/3).
Matrices Q and R. Q=1/21/201/6−1/62/3,R=(201/23/2).
Conclusion.A=QR with Q having orthonormal columns and R upper triangular.