# dlaed5.f - Man Page

## Synopsis

### Functions/Subroutines

subroutine **dlaed5** (I, D, Z, DELTA, RHO, DLAM)**DLAED5** used by sstedc. Solves the 2-by-2 secular equation.

## Function/Subroutine Documentation

### subroutine dlaed5 (integer I, double precision, dimension( 2 ) D, double precision, dimension( 2 ) Z, double precision, dimension( 2 ) DELTA, double precision RHO, double precision DLAM)

**DLAED5** used by sstedc. Solves the 2-by-2 secular equation.

**Purpose:**

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.

**Parameters:***I*I is INTEGER The index of the eigenvalue to be computed. I = 1 or I = 2.

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

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

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

*RHO*RHO is DOUBLE PRECISION The scalar in the symmetric updating formula.

*DLAM*DLAM is DOUBLE PRECISION The computed lambda_I, the I-th updated eigenvalue.

**Author:**Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date:**December 2016

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

Definition at line 110 of file dlaed5.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page dlaed5(3) is an alias of dlaed5.f(3).

Tue Nov 14 2017 Version 3.8.0 LAPACK