An Algorithm for the Ill-Conditioned Generalized Eigenvalue Problem
George J. Fix, Richard M. Heiberger · SIAM Journal on Numerical Analysis · 1972
The spectrum of $Ax - \lambda Bx = 0$ consists of stable and unstable eigenvalues, which undergo, respectively, small and large changes in response to small changes in A and B. The algorithm isolates and accurately computes the eigenspace associated with the stable eigenvalues.