DLAEXC (3)  Linux Manuals
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.
NN is INTEGER The order of the matrix T. N >= 0.
TT 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.
LDTLDT is INTEGER The leading dimension of the array T. LDT >= max(1,N).
QQ 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.
LDQLDQ is INTEGER The leading dimension of the array Q. LDQ >= 1; and if WANTQ is .TRUE., LDQ >= N.
J1J1 is INTEGER The index of the first row of the first block T11.
N1N1 is INTEGER The order of the first block T11. N1 = 0, 1 or 2.
N2N2 is INTEGER The order of the second block T22. N2 = 0, 1 or 2.
WORKWORK is DOUBLE PRECISION array, dimension (N)
INFOINFO 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
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