QRDecomposition コマンド

QRDecomposition({{1,2},{3,4}}) は，
行列 $\begin{pmatrix}\frac1{\sqrt{10}}&\frac{\frac35}{\frac{\sqrt{10}}5}\\\frac3{\sqrt{10}}&\frac{\frac15}{\frac{\sqrt{10}}{5}}\end{pmatrix}$, $\begin{pmatrix}\sqrt{10}&\frac75\sqrt{10}\\0&\frac{\sqrt{10}}5\end{pmatrix}$を返す．