Issue
EPL
Volume 78, Number 1, April 2007
Article Number 12001
Number of page(s) 5
Section Nuclear Physics
DOI http://dx.doi.org/10.1209/0295-5075/78/12001
Published online 09 March 2007
EPL, 78 (2007) 12001
DOI: 10.1209/0295-5075/78/12001

Reduction of the RPA eigenvalue problem and a generalized Cholesky decomposition for real-symmetric matrices

P. Papakonstantinou

Institut für Kernphysik, Technische Universität Darmstadt - Schlossgartenstr. 9, D-64289 Darmstadt, Germany


received 28 November 2006; accepted in final form 7 February 2007; published April 2007
published online 9 March 2007

Abstract
The particular symmetry of the random-phase-approximation (RPA) matrix has been utilized in the past to reduce the RPA eigenvalue problem into a symmetric-matrix problem of half the dimension. The condition of positive-definiteness of at least one of the matrices $A\pm B$ has been imposed (where A and B are the submatrices of the RPA matrix) so that, e.g., its square root can be found by Cholesky decomposition. In this work, alternative methods are pointed out to reduce the RPA problem to a real (not symmetric, in general) problem of half the dimension, with the condition of positive-definiteness relaxed. One of the methods relies on a generalized Cholesky decomposition, valid for non-singular real symmetric matrices. The algorithm is described and a corresponding routine in C is given.

PACS
21.60.Jz - Hartree-Fock and random-phase approximations.
02.60.Dc - Numerical linear algebra.
02.10.Yn - Matrix theory.

© Europhysics Letters Association 2007