# dlaed5 (l) - Linux Manuals

## dlaed5: subroutine compute 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

## NAME

DLAED5 - subroutine compute 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.

## FURTHER DETAILS

Based on contributions byRen-Cang Li, Computer Science Division, University of California

at Berkeley, USA