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slaed5.f(3) LAPACK slaed5.f(3)

NAME

slaed5.f -

SYNOPSIS

Functions/Subroutines


subroutine slaed5 (I, D, Z, DELTA, RHO, DLAM)
SLAED5 used by sstedc. Solves the 2-by-2 secular equation.

Function/Subroutine Documentation

subroutine slaed5 (integerI, real, dimension( 2 )D, real, dimension( 2 )Z, real, dimension( 2 )DELTA, realRHO, realDLAM)

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

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:

I


I is INTEGER
The index of the eigenvalue to be computed. I = 1 or I = 2.

D


D is REAL array, dimension (2)
The original eigenvalues. We assume D(1) < D(2).

Z


Z is REAL array, dimension (2)
The components of the updating vector.

DELTA


DELTA is REAL array, dimension (2)
The vector DELTA contains the information necessary
to construct the eigenvectors.

RHO


RHO is REAL
The scalar in the symmetric updating formula.

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.

Date:

September 2012

Contributors:

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

Definition at line 109 of file slaed5.f.

Author

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Tue Sep 25 2012 Version 3.4.2