DLAED5 (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 DLAED5( I, D, Z, DELTA, RHO, DLAM )

      INTEGER        I

      DOUBLE         PRECISION DLAM, RHO

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

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

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

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

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