
ctgex2.f(3) LAPACK ctgex2.f(3)
NAME
ctgex2.f 
SYNOPSIS
Functions/Subroutines
subroutine ctgex2 (WANTQ, WANTZ, N, A, LDA, B, LDB, Q, LDQ, Z, LDZ, J1, INFO)
CTGEX2 swaps adjacent diagonal blocks in an upper (quasi) triangular matrix pair by an
unitary equivalence transformation.
Function/Subroutine Documentation
subroutine ctgex2 (logicalWANTQ, logicalWANTZ, integerN, complex, dimension( lda, * )A,
integerLDA, complex, dimension( ldb, * )B, integerLDB, complex, dimension( ldq, * )Q,
integerLDQ, complex, dimension( ldz, * )Z, integerLDZ, integerJ1, integerINFO)
CTGEX2 swaps adjacent diagonal blocks in an upper (quasi) triangular matrix pair by an
unitary equivalence transformation.
Purpose:
CTGEX2 swaps adjacent diagonal 1 by 1 blocks (A11,B11) and (A22,B22)
in an upper triangular matrix pair (A, B) by an unitary equivalence
transformation.
(A, B) must be in generalized Schur canonical form, that is, A and
B are both upper triangular.
Optionally, the matrices Q and Z of generalized Schur vectors are
updated.
Q(in) * A(in) * Z(in)**H = Q(out) * A(out) * Z(out)**H
Q(in) * B(in) * Z(in)**H = Q(out) * B(out) * Z(out)**H
Parameters:
WANTQ
WANTQ is LOGICAL
.TRUE. : update the left transformation matrix Q;
.FALSE.: do not update Q.
WANTZ
WANTZ is LOGICAL
.TRUE. : update the right transformation matrix Z;
.FALSE.: do not update Z.
N
N is INTEGER
The order of the matrices A and B. N >= 0.
A
A is COMPLEX arrays, dimensions (LDA,N)
On entry, the matrix A in the pair (A, B).
On exit, the updated matrix A.
LDA
LDA is INTEGER
The leading dimension of the array A. LDA >= max(1,N).
B
B is COMPLEX arrays, dimensions (LDB,N)
On entry, the matrix B in the pair (A, B).
On exit, the updated matrix B.
LDB
LDB is INTEGER
The leading dimension of the array B. LDB >= max(1,N).
Q
Q is COMPLEX array, dimension (LDZ,N)
If WANTQ = .TRUE, on entry, the unitary matrix Q. On exit,
the updated matrix Q.
Not referenced if WANTQ = .FALSE..
LDQ
LDQ is INTEGER
The leading dimension of the array Q. LDQ >= 1;
If WANTQ = .TRUE., LDQ >= N.
Z
Z is COMPLEX array, dimension (LDZ,N)
If WANTZ = .TRUE, on entry, the unitary matrix Z. On exit,
the updated matrix Z.
Not referenced if WANTZ = .FALSE..
LDZ
LDZ is INTEGER
The leading dimension of the array Z. LDZ >= 1;
If WANTZ = .TRUE., LDZ >= N.
J1
J1 is INTEGER
The index to the first block (A11, B11).
INFO
INFO is INTEGER
=0: Successful exit.
=1: The transformed matrix pair (A, B) would be too far
from generalized Schur form; the problem is ill
conditioned.
Author:
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
September 2012
Further Details:
In the current code both weak and strong stability tests are performed. The user can
omit the strong stability test by changing the internal logical parameter WANDS to
.FALSE.. See ref. [2] for details.
Contributors:
Bo Kagstrom and Peter Poromaa, Department of Computing Science, Umea University, S901
87 Umea, Sweden.
References:
[1] B. Kagstrom; A Direct Method for Reordering Eigenvalues in the Generalized Real
Schur Form of a Regular Matrix Pair (A, B), in M.S. Moonen et al (eds), Linear Algebra
for Large Scale and RealTime Applications, Kluwer Academic Publ. 1993, pp 195218.
[2] B. Kagstrom and P. Poromaa; Computing Eigenspaces with Specified Eigenvalues of a
Regular Matrix Pair (A, B) and Condition Estimation: Theory, Algorithms and Software,
Report UMINF94.04, Department of Computing Science, Umea University, S901 87 Umea,
Sweden, 1994. Also as LAPACK Working Note 87. To appear in Numerical Algorithms, 1996.
Definition at line 190 of file ctgex2.f.
Author
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Version 3.4.2 Tue Sep 25 2012 ctgex2.f(3) 
