Computes axiality and rhombicity of a symmetric 3x3 interaction tensor from the corresponding matrix.
M - a real symmetric 3x3 matrix
iso - isotropic part of the interaction, defined as (xx+yy+zz)/3 in terms of eigenvaues ax - interaction axiality, defined as zz-(xx+yy)/2 in terms of eigenvalues rh - interaction rhombicity, defined as (xx-yy) in terms of eigenvalues
1. Eigenvalues [xx yy zz] are sorted in Mehring order, that is xx<=yy<=zz.
2. Euler angles are not returned because the transformation in question is ill-defined.
Version 2.1, authors: Ilya Kuprov