# CentOS 7.0 - man page for slasd5 (centos section 3)

```slasd5.f(3)							      LAPACK							       slasd5.f(3)

NAME
slasd5.f -

SYNOPSIS
Functions/Subroutines
subroutine slasd5 (I, D, Z, DELTA, RHO, DSIGMA, WORK)
SLASD5 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 slasd5 (integerI, real, dimension( 2 )D, real, dimension( 2 )Z, real, dimension( 2 )DELTA, realRHO, realDSIGMA, real, dimension( 2
)WORK)
SLASD5 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 REAL array, dimension (2)
The original eigenvalues.  We assume 0 <= D(1) < D(2).

Z

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

DELTA

DELTA is REAL 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 REAL
The scalar in the symmetric updating formula.

DSIGMA

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

WORK

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

Author:
Univ. of Tennessee

Univ. of California Berkeley

NAG Ltd.

Date:
September 2012

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

Definition at line 117 of file slasd5.f.

Author
Generated automatically by Doxygen for LAPACK from the source code.

Version 3.4.2							  Tue Sep 25 2012						       slasd5.f(3)```