Let H = \begin{pmatrix}1 &0& 0\\ −1 &−2 &−1\\ 0 &2& 1\end{pmatrix}.
(a) Apply the “vanilla” QR iteration to H.
(b) Apply the the single shift QR iteration on H.
(a) The “vanilla” QR iteration fails to converge.
(b) H − I = QR = \begin{pmatrix}0 &0 &1\\ −1 &0& 0\\ 0 &1& 0\end{pmatrix} \begin{pmatrix}1 &3& 1\\ 0 &2& 0\\ 0 &0& 0\end{pmatrix} and RQ + I = \begin{pmatrix}−2& 1 &1\\ −2 &1& 0\\ 0 &0& 1\end{pmatrix}.