Solver for generalized eigenvalue problem (linear buckling analysis)

I am using Karamba3D to perform a linear buckling analysis.
From reading the manual, I could not figure out what kind of solver is used for solving a generalized eigenvalue problem. (Is the solver subspace method? or Lanczos method?).
I would appreciate it if you could enlighten me.
Thank you.

Hello @tKMR ,
Karamba3D uses arpack which is based on the Implicitly Restarted Arnoldi Method.
– Clemens

Thank you so much for your quick response.