# DLANV2 (3) - Linux Man Pages

dlanv2.f -

## SYNOPSIS

### Functions/Subroutines

subroutine dlanv2 (A, B, C, D, RT1R, RT1I, RT2R, RT2I, CS, SN)
DLANV2 computes the Schur factorization of a real 2-by-2 nonsymmetric matrix in standard form.

## Function/Subroutine Documentation

### subroutine dlanv2 (double precisionA, double precisionB, double precisionC, double precisionD, double precisionRT1R, double precisionRT1I, double precisionRT2R, double precisionRT2I, double precisionCS, double precisionSN)

DLANV2 computes the Schur factorization of a real 2-by-2 nonsymmetric matrix in standard form.

Purpose:

``` DLANV2 computes the Schur factorization of a real 2-by-2 nonsymmetric
matrix in standard form:

[ A  B ] = [ CS -SN ] [ AA  BB ] [ CS  SN ]
[ C  D ]   [ SN  CS ] [ CC  DD ] [-SN  CS ]

where either
1) CC = 0 so that AA and DD are real eigenvalues of the matrix, or
2) AA = DD and BB*CC < 0, so that AA + or - sqrt(BB*CC) are complex
conjugate eigenvalues.
```

Parameters:

A

```          A is DOUBLE PRECISION
```

B

```          B is DOUBLE PRECISION
```

C

```          C is DOUBLE PRECISION
```

D

```          D is DOUBLE PRECISION
On entry, the elements of the input matrix.
On exit, they are overwritten by the elements of the
standardised Schur form.
```

RT1R

```          RT1R is DOUBLE PRECISION
```

RT1I

```          RT1I is DOUBLE PRECISION
```

RT2R

```          RT2R is DOUBLE PRECISION
```

RT2I

```          RT2I is DOUBLE PRECISION
The real and imaginary parts of the eigenvalues. If the
eigenvalues are a complex conjugate pair, RT1I > 0.
```

CS

```          CS is DOUBLE PRECISION
```

SN

```          SN is DOUBLE PRECISION
Parameters of the rotation matrix.
```

Author:

Univ. of Tennessee

Univ. of California Berkeley

NAG Ltd.

Date:

September 2012

Further Details:

```  Modified by V. Sima, Research Institute for Informatics, Bucharest,
Romania, to reduce the risk of cancellation errors,
when computing real eigenvalues, and to ensure, if possible, that
abs(RT1R) >= abs(RT2R).
```

Definition at line 128 of file dlanv2.f.

## Author

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