1DLAED5(1)                LAPACK routine (version 3.2)                DLAED5(1)
2
3
4

NAME

6       DLAED5 - subroutine compute the I-th eigenvalue of a symmetric rank-one
7       modification of a 2-by-2 diagonal matrix   diag( D ) + RHO  The  diago‐
8       nal  elements in the array D are assumed to satisfy   D(i) < D(j) for i
9       < j
10

SYNOPSIS

12       SUBROUTINE DLAED5( I, D, Z, DELTA, RHO, DLAM )
13
14           INTEGER        I
15
16           DOUBLE         PRECISION DLAM, RHO
17
18           DOUBLE         PRECISION D( 2 ), DELTA( 2 ), Z( 2 )
19

PURPOSE

21       This subroutine computes the I-th eigenvalue of  a  symmetric  rank-one
22       modification  of  a  2-by-2  diagonal matrix We also assume RHO > 0 and
23       that the Euclidean norm of the vector Z is one.
24

ARGUMENTS

26       I      (input) INTEGER
27              The index of the eigenvalue to be computed.  I = 1 or I = 2.
28
29       D      (input) DOUBLE PRECISION array, dimension (2)
30              The original eigenvalues.  We assume D(1) < D(2).
31
32       Z      (input) DOUBLE PRECISION array, dimension (2)
33              The components of the updating vector.
34
35       DELTA  (output) DOUBLE PRECISION array, dimension (2)
36              The vector DELTA contains the information necessary to construct
37              the eigenvectors.
38
39       RHO    (input) DOUBLE PRECISION
40              The scalar in the symmetric updating formula.
41
42       DLAM   (output) DOUBLE PRECISION
43              The computed lambda_I, the I-th updated eigenvalue.
44

FURTHER DETAILS

46       Based on contributions by
47          Ren-Cang Li, Computer Science Division, University of California
48          at Berkeley, USA
49
50
51
52 LAPACK routine (version 3.2)    November 2008                       DLAED5(1)