John von Neumann Institute for Computing Direct Solvers for Symmetric Eigenvalue Problems Bruno Lang published in Modern Methods and Algorithms of Quantum Chemistry, Proceedings, Second Edition, J. Grotendorst (Ed.), John von Neumann Institute for Computing, Julich,¨ NIC Series, Vol. 3, ISBN 3-00-005834-6, pp. 231-259, 2000. c 2000 by John von Neumann Institute for Computing Permission to make digital or hard copies of portions of this work for personal or classroom use is granted provided that the copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise requires prior specific permission by the publisher mentioned above. http://www.fz-juelich.de/nic-series/ DIRECT SOLVERS FOR SYMMETRIC EIGENVALUE PROBLEMS BRUNO LANG Aachen University of Technology Computing Center Seffenter Weg 23, 52074 Aachen, Germany E-mail:
[email protected] This article reviews classical and recent direct methods for computing eigenvalues and eigenvectors of symmetric full or banded matrices. The ideas underlying the methods are presented, and the properties of the algorithms with respect to ac- curacy and performance are discussed. Finally, pointers to relevant software are given. This article reviews classical, as well as recent state-of-the-art, direct solvers for standard and generalized symmetric eigenvalue problems. In Section 1 we explain what direct solvers for symmetric eigenvalue problems are. Section 2 describes what we may reasonably expect from an eigenvalue solver in terms of accuracy and how algorithms should be structured in order to minimize the computing time, and introduces two basic tools on which most eigensolvers are based, namely similarity transformations and deflation.