slaexc.f File Reference

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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.

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Function/Subroutine Documentation

subroutine slaexc	(	logical	WANTQ,
		integer	N,
		real, dimension( ldt, * )	T,
		integer	LDT,
		real, dimension( ldq, * )	Q,
		integer	LDQ,
		integer	J1,
		integer	N1,
		integer	N2,
		real, dimension( * )	WORK,
		integer	INFO
	)

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

Download SLAEXC + dependencies [TGZ] [ZIP] [TXT]

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:

[in]	WANTQ	WANTQ is LOGICAL = .TRUE. : accumulate the transformation in the matrix Q; = .FALSE.: do not accumulate the transformation.
[in]	N	N is INTEGER The order of the matrix T. N >= 0.
[in,out]	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.
[in]	LDT	LDT is INTEGER The leading dimension of the array T. LDT >= max(1,N).
[in,out]	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.
[in]	LDQ	LDQ is INTEGER The leading dimension of the array Q. LDQ >= 1; and if WANTQ is .TRUE., LDQ >= N.
[in]	J1	J1 is INTEGER The index of the first row of the first block T11.
[in]	N1	N1 is INTEGER The order of the first block T11. N1 = 0, 1 or 2.
[in]	N2	N2 is INTEGER The order of the second block T22. N2 = 0, 1 or 2.
[out]	WORK	WORK is REAL array, dimension (N)
[out]	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.

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