!>
!> 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.
!> 

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.
!> 

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

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