# zlags2.f man page

zlags2.f —

## Synopsis

### Functions/Subroutines

subroutinezlags2(UPPER, A1, A2, A3, B1, B2, B3, CSU, SNU, CSV, SNV, CSQ, SNQ)ZLAGS2

## Function/Subroutine Documentation

### subroutine zlags2 (logicalUPPER, double precisionA1, complex*16A2, double precisionA3, double precisionB1, complex*16B2, double precisionB3, double precisionCSU, complex*16SNU, double precisionCSV, complex*16SNV, double precisionCSQ, complex*16SNQ)

**ZLAGS2**

**Purpose:**

```
ZLAGS2 computes 2-by-2 unitary matrices U, V and Q, such
that if ( UPPER ) then
U**H *A*Q = U**H *( A1 A2 )*Q = ( x 0 )
( 0 A3 ) ( x x )
and
V**H*B*Q = V**H *( B1 B2 )*Q = ( x 0 )
( 0 B3 ) ( x x )
or if ( .NOT.UPPER ) then
U**H *A*Q = U**H *( A1 0 )*Q = ( x x )
( A2 A3 ) ( 0 x )
and
V**H *B*Q = V**H *( B1 0 )*Q = ( x x )
( B2 B3 ) ( 0 x )
where
U = ( CSU SNU ), V = ( CSV SNV ),
( -SNU**H CSU ) ( -SNV**H CSV )
Q = ( CSQ SNQ )
( -SNQ**H CSQ )
The rows of the transformed A and B are parallel. Moreover, if the
input 2-by-2 matrix A is not zero, then the transformed (1,1) entry
of A is not zero. If the input matrices A and B are both not zero,
then the transformed (2,2) element of B is not zero, except when the
first rows of input A and B are parallel and the second rows are
zero.
```

**Parameters:**

*UPPER*

```
UPPER is LOGICAL
= .TRUE.: the input matrices A and B are upper triangular.
= .FALSE.: the input matrices A and B are lower triangular.
```

*A1*

`A1 is DOUBLE PRECISION`

*A2*

`A2 is COMPLEX*16`

*A3*

```
A3 is DOUBLE PRECISION
On entry, A1, A2 and A3 are elements of the input 2-by-2
upper (lower) triangular matrix A.
```

*B1*

`B1 is DOUBLE PRECISION`

*B2*

`B2 is COMPLEX*16`

*B3*

```
B3 is DOUBLE PRECISION
On entry, B1, B2 and B3 are elements of the input 2-by-2
upper (lower) triangular matrix B.
```

*CSU*

`CSU is DOUBLE PRECISION`

*SNU*

```
SNU is COMPLEX*16
The desired unitary matrix U.
```

*CSV*

`CSV is DOUBLE PRECISION`

*SNV*

```
SNV is COMPLEX*16
The desired unitary matrix V.
```

*CSQ*

`CSQ is DOUBLE PRECISION`

*SNQ*

```
SNQ is COMPLEX*16
The desired unitary matrix Q.
```

**Author:**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date:**

November 2011

Definition at line 158 of file zlags2.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

zlags2(3) is an alias of zlags2.f(3).