SLAED5 (3lapack)

subroutine computes the I-th eigenvalue of a symmetric rank-one modification of a 2-by-2 diagonal matrix diag( D ) + RHO The diagonal elements in the array D are assumed to satisfy D(i) < D(j) for i < j

SYNOPSIS

  SUBROUTINE SLAED5( I, D, Z, DELTA, RHO, DLAM )

      INTEGER        I

      REAL           DLAM, RHO

      REAL           D( 2 ), DELTA( 2 ), Z( 2 )

PURPOSE

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

  We also assume RHO > 0 and that the Euclidean norm of the vector Z is one.

ARGUMENTS

  I      (input) INTEGER
         The index of the eigenvalue to be computed.  I = 1 or I = 2.

  D      (input) REAL array, dimension (2)
         The original eigenvalues.  We assume D(1) < D(2).

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

  DELTA  (output) REAL array, dimension (2)
         The vector DELTA contains the information necessary to construct the
         eigenvectors.

  RHO    (input) REAL
         The scalar in the symmetric updating formula.

  DLAM   (output) REAL
         The computed lambda_I, the I-th updated eigenvalue.