common invariant subspaces of two matrices

[mjacobi]

Hi all,

 

Given two quadratic matrices A and B. Does anyone know if there exist some efficient (polynomial) algorithm for identifying subspaces that are invariant under both A and B?

 

Thanks for help on this

[Dr. Jekyll]

I remember something about generalized eigenvalue problem in connection to this, but I can't place it. Think it was a presentation at some conference I attended some years ago.