slasd53

!>
!> 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.
!> 

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.
!> 

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