SLAEXC (3) Linux Manual 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

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