Glued Matrices and the MRRR Algorithm

Inderjit Dhillon, Beresford Parlett, Christof Vömel

Abstract:   During the last ten years, Dhillon and Parlett devised a new algorithm (multiple relatively robust representations (MRRR)) for computing numerically orthogonal eigenvectors of a symmetric tridiagonal matrix T with O(n^2) cost. It has been incorporated into LAPACK version 3.0 as routine stegr. We have discovered that the MRRR algorithm can fail in extreme cases. Sometimes eigenvalues agree to working accuracy and MRRR cannot compute orthogonal eigenvectors for them. In this paper, we describe and analyze these failures and various remedies.

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  • Glued Matrices and the MRRR Algorithm (pdf)
    I. Dhillon, B. Parlett, C. Vömel.
    SIAM Journal on Scientific Computing 27(2), pp. 496-510, October 2005.