Other Jacobi-related methods?

[jagot]

I actually came back to this package because I found https://github.com/JLTastet/TakagiFactorization.jl (LGPL3), based on https://arxiv.org/pdf/physics/0607103.pdf, which uses the Jacobi iterations, but different 2x2 kernels to compute the eigendecomposition, Takagi, SVD etc. I need the full (dense) eigendecomposition of a complex symmetric matrix (absorbing boundary conditions leads to these kind of matrices), and I wondered if such methods could have a place here? Specifically, the matrix is a SymTridiagonal{<:Complex}, so it seems some nice special-casing could be done.