dlasd5.f man page

dlasd5.f —

Synopsis

Functions/Subroutines

subroutine dlasd5 (I, D, Z, DELTA, RHO, DSIGMA, WORK)
DLASD5 computes the square root of the i-th eigenvalue of a positive symmetric rank-one modification of a 2-by-2 diagonal matrix. Used by sbdsdc.

Function/Subroutine Documentation

subroutine dlasd5 (integerI, double precision, dimension( 2 )D, double precision, dimension( 2 )Z, double precision, dimension( 2 )DELTA, double precisionRHO, double precisionDSIGMA, double precision, dimension( 2 )WORK)

DLASD5 computes the square root of the i-th eigenvalue of a positive symmetric rank-one modification of a 2-by-2 diagonal matrix. Used by sbdsdc.

Purpose:

This subroutine computes the square root of the I-th eigenvalue
of a positive symmetric rank-one modification of a 2-by-2 diagonal
matrix

           diag( D ) * diag( D ) +  RHO * Z * transpose(Z) .

The diagonal entries in the array D are assumed to satisfy

           0 <= 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 DOUBLE PRECISION array, dimension ( 2 )
The original eigenvalues.  We assume 0 <= D(1) < D(2).

Z

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

DELTA

 DELTA is DOUBLE PRECISION array, dimension ( 2 )
Contains (D(j) - sigma_I) in its  j-th component.
The vector DELTA contains the information necessary
to construct the eigenvectors.

RHO

 RHO is DOUBLE PRECISION
The scalar in the symmetric updating formula.

DSIGMA

 DSIGMA is DOUBLE PRECISION
The computed sigma_I, the I-th updated eigenvalue.

WORK

 WORK is DOUBLE PRECISION array, dimension ( 2 )
WORK contains (D(j) + sigma_I) in its  j-th component.

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 117 of file dlasd5.f.

Author

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Referenced By

dlasd5(3) is an alias of dlasd5.f(3).

Sat Nov 16 2013 Version 3.4.2 LAPACK