ctrexc()

subroutine ctrexc	(	character	compq,
		integer	n,
		complex, dimension( ldt, * )	t,
		integer	ldt,
		complex, dimension( ldq, * )	q,
		integer	ldq,
		integer	ifst,
		integer	ilst,
		integer	info )

CTREXC

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Purpose:

!>
!> CTREXC reorders the Schur factorization of a complex matrix
!> A = Q*T*Q**H, so that the diagonal element of T with row index IFST
!> is moved to row ILST.
!>
!> The Schur form T is reordered by a unitary similarity transformation
!> Z**H*T*Z, and optionally the matrix Q of Schur vectors is updated by
!> postmultiplying it with Z.
!> 

Parameters

[in]	COMPQ	!> COMPQ is CHARACTER*1 !> = 'V': update the matrix Q of Schur vectors; !> = 'N': do not update Q. !>
[in]	N	!> N is INTEGER !> The order of the matrix T. N >= 0. !> If N == 0 arguments ILST and IFST may be any value. !>
[in,out]	T	!> T is COMPLEX array, dimension (LDT,N) !> On entry, the upper triangular matrix T. !> On exit, the reordered upper triangular matrix. !>
[in]	LDT	!> LDT is INTEGER !> The leading dimension of the array T. LDT >= max(1,N). !>
[in,out]	Q	!> Q is COMPLEX 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 !> unitary transformation matrix Z which reorders T. !> If COMPQ = 'N', Q is not referenced. !>
[in]	LDQ	!> LDQ is INTEGER !> The leading dimension of the array Q. LDQ >= 1, and if !> COMPQ = 'V', LDQ >= max(1,N). !>
[in]	IFST	!> IFST is INTEGER !>
[in]	ILST	!> ILST is INTEGER !> !> Specify the reordering of the diagonal elements of T: !> The element with row index IFST is moved to row ILST by a !> sequence of transpositions between adjacent elements. !> 1 <= IFST <= N; 1 <= ILST <= N. !>
[out]	INFO	!> INFO is INTEGER !> = 0: successful exit !> < 0: if INFO = -i, the i-th argument had an illegal value !>

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.