Iteration schemes for the divide - and - conquereigenvalue

We propose globally convergent iteration schemes for updating the eigenvalues of a symmetric matrix after a rank-1 modiication. Such calculations are the core of the divide-and-conquer technique for the symmetric tridiagonal eigenvalue problem. We prove the superlinear convergence right from the start of our schemes which allows us to improve the complexity bounds of 3]. The eeec-tiveness of our algorithms is connrmed by numerical results which are reported and discussed.