slaed5()

subroutine slaed5	(	integer	i,
		real, dimension( 2 )	d,
		real, dimension( 2 )	z,
		real, dimension( 2 )	delta,
		real	rho,
		real	dlam )

SLAED5 used by SSTEDC. Solves the 2-by-2 secular equation.

Download SLAED5 + dependencies [TGZ] [ZIP] [TXT]

Purpose:

!>
!> This subroutine computes the I-th eigenvalue of a symmetric rank-one
!> modification of a 2-by-2 diagonal matrix
!>
!>            diag( D )  +  RHO * Z * transpose(Z) .
!>
!> The diagonal elements in the array D are assumed to satisfy
!>
!>            D(i) < D(j)  for  i < j .
!>
!> We also assume RHO > 0 and that the Euclidean norm of the vector
!> Z is one.
!> 

Parameters

[in]	I	!> I is INTEGER !> The index of the eigenvalue to be computed. I = 1 or I = 2. !>
[in]	D	!> D is REAL array, dimension (2) !> The original eigenvalues. We assume D(1) < D(2). !>
[in]	Z	!> Z is REAL array, dimension (2) !> The components of the updating vector. !>
[out]	DELTA	!> DELTA is REAL array, dimension (2) !> The vector DELTA contains the information necessary !> to construct the eigenvectors. !>
[in]	RHO	!> RHO is REAL !> The scalar in the symmetric updating formula. !>
[out]	DLAM	!> DLAM is REAL !> The computed lambda_I, the I-th updated eigenvalue. !>

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Contributors:

Ren-Cang Li, Computer Science Division, University of California at Berkeley, USA