# dlags2.f - Man Page

SRC/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 (logical upper, double precision a1, double precision a2, double precision a3, double precision b1, double precision b2, double precision b3, double precision csu, double precision snu, double precision csv, double precision snv, double precision csq, double precision 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.

**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.

Definition at line **150** of file **dlags2.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page dlags2(3) is an alias of dlags2.f(3).

Tue Nov 28 2023 12:08:42 Version 3.12.0 LAPACK