# zlags2.f man page

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 (logical UPPER, double precision A1, complex*16 A2, double precision A3, double precision B1, complex*16 B2, double precision B3, double precision CSU, complex*16 SNU, double precision CSV, complex*16 SNV, double precision CSQ, complex*16 SNQ)

**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:**December 2016

Definition at line 160 of file zlags2.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page zlags2(3) is an alias of zlags2.f(3).

Tue Nov 14 2017 Version 3.8.0 LAPACK