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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
NAG Ltd.
Date:
November 2011
Definition at line 158 of file zlags2.f.

# Author

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