Reference:
- A Robust Eigensolver for 3 × 3 Symmetric Matrices ( https://www.geometrictools.com/Documentation/RobustEigenSymmetric3x3.pdf )
- 計算物理学２第10回：逆行列・固有値問題 ( https://wwwnucl.ph.tsukuba.ac.jp/~hinohara/compphys2-19/doc/compphys2-10.pdf )
- The Jacobi Method for Real Symmetric Matrices https://ics.p.lodz.pl/~dpuchala/JacobiNewI.pdf