# dlaed5.f man page

dlaed5.f —

## Synopsis

### Functions/Subroutines

subroutinedlaed5(I, D, Z, DELTA, RHO, DLAM)DLAED5used by sstedc. Solves the 2-by-2 secular equation.

## Function/Subroutine Documentation

### subroutine dlaed5 (integerI, double precision, dimension( 2 )D, double precision, dimension( 2 )Z, double precision, dimension( 2 )DELTA, double precisionRHO, double precisionDLAM)

**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:**

September 2012

**Contributors:**

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

Definition at line 109 of file dlaed5.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

dlaed5(3) is an alias of dlaed5.f(3).