# dlags2.f(3) [centos man page]

```dlags2.f(3)							      LAPACK							       dlags2.f(3)

NAME
dlags2.f -

SYNOPSIS
Functions/Subroutines
subroutine dlags2 (UPPER, A1, A2, A3, B1, B2, B3, CSU, SNU, CSV, SNV, CSQ, SNQ)
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.

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

NAG Ltd.

Date:
September 2012

Definition at line 152 of file dlags2.f.

Author
Generated automatically by Doxygen for LAPACK from the source code.

Version 3.4.2							  Tue Sep 25 2012						       dlags2.f(3)```

## Check Out this Related Man Page

```zlags2.f(3)							      LAPACK							       zlags2.f(3)

NAME
zlags2.f -

SYNOPSIS
Functions/Subroutines
subroutine zlags2 (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