
dlaexc.f(3) LAPACK dlaexc.f(3)
NAME
dlaexc.f 
SYNOPSIS
Functions/Subroutines
subroutine dlaexc (WANTQ, N, T, LDT, Q, LDQ, J1, N1, N2, WORK, INFO)
DLAEXC swaps adjacent diagonal blocks of a real upper quasitriangular matrix in Schur
canonical form, by an orthogonal similarity transformation.
Function/Subroutine Documentation
subroutine dlaexc (logicalWANTQ, integerN, double precision, dimension( ldt, * )T, integerLDT,
double precision, dimension( ldq, * )Q, integerLDQ, integerJ1, integerN1, integerN2,
double precision, dimension( * )WORK, integerINFO)
DLAEXC swaps adjacent diagonal blocks of a real upper quasitriangular matrix in Schur
canonical form, by an orthogonal similarity transformation.
Purpose:
DLAEXC swaps adjacent diagonal blocks T11 and T22 of order 1 or 2 in
an upper quasitriangular matrix T by an orthogonal similarity
transformation.
T must be in Schur canonical form, that is, block upper triangular
with 1by1 and 2by2 diagonal blocks; each 2by2 diagonal block
has its diagonal elemnts equal and its offdiagonal elements of
opposite sign.
Parameters:
WANTQ
WANTQ is LOGICAL
= .TRUE. : accumulate the transformation in the matrix Q;
= .FALSE.: do not accumulate the transformation.
N
N is INTEGER
The order of the matrix T. N >= 0.
T
T is DOUBLE PRECISION array, dimension (LDT,N)
On entry, the upper quasitriangular matrix T, in Schur
canonical form.
On exit, the updated matrix T, again in Schur canonical form.
LDT
LDT is INTEGER
The leading dimension of the array T. LDT >= max(1,N).
Q
Q is DOUBLE PRECISION array, dimension (LDQ,N)
On entry, if WANTQ is .TRUE., the orthogonal matrix Q.
On exit, if WANTQ is .TRUE., the updated matrix Q.
If WANTQ is .FALSE., Q is not referenced.
LDQ
LDQ is INTEGER
The leading dimension of the array Q.
LDQ >= 1; and if WANTQ is .TRUE., LDQ >= N.
J1
J1 is INTEGER
The index of the first row of the first block T11.
N1
N1 is INTEGER
The order of the first block T11. N1 = 0, 1 or 2.
N2
N2 is INTEGER
The order of the second block T22. N2 = 0, 1 or 2.
WORK
WORK is DOUBLE PRECISION array, dimension (N)
INFO
INFO is INTEGER
= 0: successful exit
= 1: the transformed matrix T would be too far from Schur
form; the blocks are not swapped and T and Q are
unchanged.
Author:
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
September 2012
Definition at line 138 of file dlaexc.f.
Author
Generated automatically by Doxygen for LAPACK from the source code.
Version 3.4.2 Tue Sep 25 2012 dlaexc.f(3) 
