Parallel computation of the eigenvalues of symmetric Toeplitz matrices through iterative methods

This paper presents a new procedure to compute many or all of the eigenvalues and eigenvectors of symmetric Toeplitz matrices. The key to this algorithm is the use of the ''Shift-and-Invert'' technique applied with iterative methods, which allows the computation of the eigenvalues close to a given real number (the ''shift''). Given an interval containing all the desired eigenvalues, this large interval can be divided in small intervals. Then, the ''Shift-and-Invert'' version of an iterative method (Lanczos method, in this paper) can be applied to each subinterval. Since the extraction of the eigenvalues of each subinterval is independent from the other subintervals, this method is highly suitable for implementation in parallel computers. This technique has been adapted to symmetric Toeplitz problems, using the symmetry exploiting Lanczos process proposed by Voss [H. Voss, A symmetry exploiting Lanczos method for symmetric Toeplitz matrices, Numerical Algorithms 25 (2000) 377-385] and using fast solvers for the Toeplitz linear systems that must be solved in each Lanczos iteration. The method compares favourably with ScaLAPACK routines, specially when not all the spectrum must be computed.