dlags2 (l)  Linux Manuals
dlags2: computes 2by2 orthogonal matrices U, V and Q, such that if ( UPPER ) then Uaq*A*Q = Uaq*( A1 A2 )*Q = ( x 0 ) ( 0 A3 ) ( x x ) and Vaq*B*Q = Vaq*( B1 B2 )*Q = ( x 0 ) ( 0 B3 ) ( x x ) or if ( .NOT.UPPER ) then Uaq*A*Q = Uaq*( A1 0 )*Q = ( x x ) ( A2 A3 ) ( 0 x ) and Vaq*B*Q = Vaq*( 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 ) Zaq denotes the transpose of Z
Command to display dlags2
manual in Linux: $ man l dlags2
NAME
DLAGS2  computes 2by2 orthogonal matrices U, V and Q, such that if ( UPPER ) then Uaq*A*Q = Uaq*( A1 A2 )*Q = ( x 0 ) ( 0 A3 ) ( x x ) and Vaq*B*Q = Vaq*( B1 B2 )*Q = ( x 0 ) ( 0 B3 ) ( x x ) or if ( .NOT.UPPER ) then Uaq*A*Q = Uaq*( A1 0 )*Q = ( x x ) ( A2 A3 ) ( 0 x ) and Vaq*B*Q = Vaq*( 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 ) Zaq denotes the transpose of Z
SYNOPSIS
 SUBROUTINE DLAGS2(

UPPER, A1, A2, A3, B1, B2, B3, CSU, SNU, CSV,
SNV, CSQ, SNQ )

LOGICAL
UPPER

DOUBLE
PRECISION A1, A2, A3, B1, B2, B3, CSQ, CSU, CSV, SNQ,
SNU, SNV
PURPOSE
DLAGS2 computes 2by2 orthogonal matrices U, V and Q, such
that if ( UPPER ) then
ARGUMENTS
 UPPER (input) LOGICAL

= .TRUE.: the input matrices A and B are upper triangular.
= .FALSE.: the input matrices A and B are lower triangular.
 A1 (input) DOUBLE PRECISION

A2 (input) DOUBLE PRECISION
A3 (input) DOUBLE PRECISION
On entry, A1, A2 and A3 are elements of the input 2by2
upper (lower) triangular matrix A.
 B1 (input) DOUBLE PRECISION

B2 (input) DOUBLE PRECISION
B3 (input) DOUBLE PRECISION
On entry, B1, B2 and B3 are elements of the input 2by2
upper (lower) triangular matrix B.
 CSU (output) DOUBLE PRECISION

SNU (output) DOUBLE PRECISION
The desired orthogonal matrix U.
 CSV (output) DOUBLE PRECISION

SNV (output) DOUBLE PRECISION
The desired orthogonal matrix V.
 CSQ (output) DOUBLE PRECISION

SNQ (output) DOUBLE PRECISION
The desired orthogonal matrix Q.
Pages related to dlags2
 dlags2 (3)
 dlag2 (l)  computes the eigenvalues of a 2 x 2 generalized eigenvalue problem A  w B, with scaling as necessary to avoid over/underflow
 dlag2s (l)  converts a DOUBLE PRECISION matrix, SA, to a SINGLE PRECISION matrix, A
 dlagtf (l)  factorizes the matrix (T  lambda*I), where T is an n by n tridiagonal matrix and lambda is a scalar, as T  lambda*I = PLU,
 dlagtm (l)  performs a matrixvector product of the form B := alpha * A * X + beta * B where A is a tridiagonal matrix of order N, B and X are N by NRHS matrices, and alpha and beta are real scalars, each of which may be 0., 1., or 1
 dlagts (l)  may be used to solve one of the systems of equations (T  lambda*I)*x = y or (T  lambda*I)aq*x = y,
 dlagv2 (l)  computes the Generalized Schur factorization of a real 2by2 matrix pencil (A,B) where B is upper triangular
 dla_gbamv (l)  performs one of the matrixvector operations y := alpha*abs(A)*abs(x) + beta*abs(y),