2階tensor
行列のことだと思っておけばいい……わけではなかったりするtakker.icon takker.iconの区別
$ \begin{aligned}\bm{A} = &A_{00}\bm{e}_0\otimes\bm{e'}_0+A_{01}\bm{e}_0\otimes\bm{e'}_1+A_{02}\bm{e}_0\otimes\bm{e'}_2+\\&A_{10}\bm{e}_1\otimes\bm{e'}_0+A_{11}\bm{e}_1\otimes\bm{e'}_1+A_{12}\bm{e}_1\otimes\bm{e'}_2+\\&A_{20}\bm{e}_2\otimes\bm{e'}_0+A_{21}\bm{e}_2\otimes\bm{e'}_1+A_{22}\bm{e}_2\otimes\bm{e'}_2\end{aligned}
$ \begin{pmatrix}A_{00}&A_{01}&A_{02}\\A_{10}&A_{11}&A_{12}\\A_{20}&A_{21}&A_{22}\end{pmatrix}=[\bm{A}]^\mathcal{ST}