dlaed5.f File Reference

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Functions/Subroutines
subroutine	dlaed5 (I, D, Z, DELTA, RHO, DLAM)
	DLAED5 used by sstedc. Solves the 2-by-2 secular equation.

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Function/Subroutine Documentation

subroutine dlaed5	(	integer	I,
		double precision, dimension( 2 )	D,
		double precision, dimension( 2 )	Z,
		double precision, dimension( 2 )	DELTA,
		double precision	RHO,
		double precision	DLAM
	)

DLAED5 used by sstedc. Solves the 2-by-2 secular equation.

Download DLAED5 + 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 DOUBLE PRECISION array, dimension (2) The original eigenvalues. We assume D(1) < D(2).
[in]	Z	Z is DOUBLE PRECISION array, dimension (2) The components of the updating vector.
[out]	DELTA	DELTA is DOUBLE PRECISION array, dimension (2) The vector DELTA contains the information necessary to construct the eigenvectors.
[in]	RHO	RHO is DOUBLE PRECISION The scalar in the symmetric updating formula.
[out]	DLAM	DLAM is DOUBLE PRECISION 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 dlaed5.f.

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