# clags2.f - Man Page

SRC/clags2.f

## Synopsis

### Functions/Subroutines

subroutine **clags2** (upper, a1, a2, a3, b1, b2, b3, csu, snu, csv, snv, csq, snq)**CLAGS2**

## Function/Subroutine Documentation

### subroutine clags2 (logical upper, real a1, complex a2, real a3, real b1, complex b2, real b3, real csu, complex snu, real csv, complex snv, real csq, complex snq)

**CLAGS2**

**Purpose:**

CLAGS2 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 REAL

*A2*A2 is COMPLEX

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

*B1*B1 is REAL

*B2*B2 is COMPLEX

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

*CSU*CSU is REAL

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

*CSV*CSV is REAL

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

*CSQ*CSQ is REAL

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

**Author**Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **156** of file **clags2.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page clags2(3) is an alias of clags2.f(3).

Tue Nov 28 2023 12:08:41 Version 3.12.0 LAPACK