
dtrexc.f(3) LAPACK dtrexc.f(3)
NAME
dtrexc.f 
SYNOPSIS
Functions/Subroutines
subroutine dtrexc (COMPQ, N, T, LDT, Q, LDQ, IFST, ILST, WORK, INFO)
DTREXC
Function/Subroutine Documentation
subroutine dtrexc (characterCOMPQ, integerN, double precision, dimension( ldt, * )T,
integerLDT, double precision, dimension( ldq, * )Q, integerLDQ, integerIFST, integerILST,
double precision, dimension( * )WORK, integerINFO)
DTREXC
Purpose:
DTREXC reorders the real Schur factorization of a real matrix
A = Q*T*Q**T, so that the diagonal block of T with row index IFST is
moved to row ILST.
The real Schur form T is reordered by an orthogonal similarity
transformation Z**T*T*Z, and optionally the matrix Q of Schur vectors
is updated by postmultiplying it with Z.
T must be in Schur canonical form (as returned by DHSEQR), that is,
block upper triangular with 1by1 and 2by2 diagonal blocks; each
2by2 diagonal block has its diagonal elements equal and its
offdiagonal elements of opposite sign.
Parameters:
COMPQ
COMPQ is CHARACTER*1
= 'V': update the matrix Q of Schur vectors;
= 'N': do not update Q.
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
Schur canonical form.
On exit, the reordered upper quasitriangular matrix, 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 COMPQ = 'V', the matrix Q of Schur vectors.
On exit, if COMPQ = 'V', Q has been postmultiplied by the
orthogonal transformation matrix Z which reorders T.
If COMPQ = 'N', Q is not referenced.
LDQ
LDQ is INTEGER
The leading dimension of the array Q. LDQ >= max(1,N).
IFST
IFST is INTEGER
ILST
ILST is INTEGER
Specify the reordering of the diagonal blocks of T.
The block with row index IFST is moved to row ILST, by a
sequence of transpositions between adjacent blocks.
On exit, if IFST pointed on entry to the second row of a
2by2 block, it is changed to point to the first row; ILST
always points to the first row of the block in its final
position (which may differ from its input value by +1 or 1).
1 <= IFST <= N; 1 <= ILST <= N.
WORK
WORK is DOUBLE PRECISION array, dimension (N)
INFO
INFO is INTEGER
= 0: successful exit
< 0: if INFO = i, the ith argument had an illegal value
= 1: two adjacent blocks were too close to swap (the problem
is very illconditioned); T may have been partially
reordered, and ILST points to the first row of the
current position of the block being moved.
Author:
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
November 2011
Definition at line 146 of file dtrexc.f.
Author
Generated automatically by Doxygen for LAPACK from the source code.
Version 3.4.2 Tue Sep 25 2012 dtrexc.f(3) 
