slaexc.f man page

slaexc.f —

Synopsis

Functions/Subroutines

subroutine slaexc (WANTQ, N, T, LDT, Q, LDQ, J1, N1, N2, WORK, INFO)
SLAEXC swaps adjacent diagonal blocks of a real upper quasi-triangular matrix in Schur canonical form, by an orthogonal similarity transformation.

Function/Subroutine Documentation

subroutine slaexc (logicalWANTQ, integerN, real, dimension( ldt, * )T, integerLDT, real, dimension( ldq, * )Q, integerLDQ, integerJ1, integerN1, integerN2, real, dimension( * )WORK, integerINFO)

SLAEXC swaps adjacent diagonal blocks of a real upper quasi-triangular matrix in Schur canonical form, by an orthogonal similarity transformation.

Purpose:

SLAEXC swaps adjacent diagonal blocks T11 and T22 of order 1 or 2 in
an upper quasi-triangular matrix T by an orthogonal similarity
transformation.

T must be in Schur canonical form, that is, block upper triangular
with 1-by-1 and 2-by-2 diagonal blocks; each 2-by-2 diagonal block
has its diagonal elemnts equal and its off-diagonal 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 REAL array, dimension (LDT,N)
On entry, the upper quasi-triangular 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 REAL 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 REAL 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 slaexc.f.

Author

Generated automatically by Doxygen for LAPACK from the source code.

Referenced By

slaexc(3) is an alias of slaexc.f(3).

Sat Nov 16 2013 Version 3.4.2 LAPACK