compute Eigenvalues and -vectors in 1-3d without LAPACK
When dealing with small matrices calling LAPACK to calculate Eigenvalues and Eigenvectors can be quite slow. 1d- and 2d-specializations are quite straightforward, for the 3d-specialization I´m using the approach presented in https://www.geometrictools.com/Documentation/RobustEigenSymmetric3x3.pdf.
Edited by Christian Engwer