# dlags2.f man page

dlags2.f —

## Synopsis

### Functions/Subroutines

subroutinedlags2(UPPER, A1, A2, A3, B1, B2, B3, CSU, SNU, CSV, SNV, CSQ, SNQ)DLAGS2computes 2-by-2 orthogonal matrices U, V, and Q, and applies them to matrices A and B such that the rows of the transformed A and B are parallel.

## Function/Subroutine Documentation

### subroutine dlags2 (logicalUPPER, double precisionA1, double precisionA2, double precisionA3, double precisionB1, double precisionB2, double precisionB3, double precisionCSU, double precisionSNU, double precisionCSV, double precisionSNV, double precisionCSQ, double precisionSNQ)

**DLAGS2** computes 2-by-2 orthogonal matrices U, V, and Q, and applies them to matrices A and B such that the rows of the transformed A and B are parallel.

**Purpose:**

```
DLAGS2 computes 2-by-2 orthogonal matrices U, V and Q, such
that if ( UPPER ) then
U**T *A*Q = U**T *( A1 A2 )*Q = ( x 0 )
( 0 A3 ) ( x x )
and
V**T*B*Q = V**T *( B1 B2 )*Q = ( x 0 )
( 0 B3 ) ( x x )
or if ( .NOT.UPPER ) then
U**T *A*Q = U**T *( A1 0 )*Q = ( x x )
( A2 A3 ) ( 0 x )
and
V**T*B*Q = V**T*( B1 0 )*Q = ( x x )
( B2 B3 ) ( 0 x )
The rows of the transformed A and B are parallel, where
U = ( CSU SNU ), V = ( CSV SNV ), Q = ( CSQ SNQ )
( -SNU CSU ) ( -SNV CSV ) ( -SNQ CSQ )
Z**T denotes the transpose of Z.
```

**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 DOUBLE PRECISION`

*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 DOUBLE PRECISION`

*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 DOUBLE PRECISION
The desired orthogonal matrix U.
```

*CSV*

`CSV is DOUBLE PRECISION`

*SNV*

```
SNV is DOUBLE PRECISION
The desired orthogonal matrix V.
```

*CSQ*

`CSQ is DOUBLE PRECISION`

*SNQ*

```
SNQ is DOUBLE PRECISION
The desired orthogonal matrix Q.
```

**Author:**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date:**

September 2012

Definition at line 152 of file dlags2.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

dlags2(3) is an alias of dlags2.f(3).