◆ ztrexc()

Reordering of Schur factorization of complex matrix

Purpose: This routine 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	= 'V': Update the matrix Q of Schur vectors. = 'N': Do not update Q.
[in]	n	Order of the matrix T. (n >= 0) (If n = 0, returns without computation)
[in]	ldt	Leading dimension of the two dimensional array t[][]. (ldt >= max(1, n))
[in,out]	t[][]	Array t[lt][ldt] (lt >= n) [in] The upper triangular matrix T. [out] The reordered upper triangular matrix.
[in]	ldq	Leading dimension of the two dimensional array q[][]. (ldq >= 1 if compq = 'N', ldq >= max(1, n) if compq = 'V')
[in,out]	q[][]	Array q[lq][ldq] (lq >= n) If compq = 'V', [in] The matrix Q of Schur vectors. [out] Q has been postmultiplied by the unitary transformation matrix Z which reorders T. If compq = 'N', q[][] is not referenced.
[in]	ifst
[in]	ilst	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	= 0: Successful exit = -1: The argument compq had an illegal value (copq != 'V' nor 'N') = -2: The argument n had an illegal value (n < 0) = -3: The argument ldt had an illegal value (ldt < max(1, n)) = -5: The argument ldq had an illegal value (ldq too small) = -7: The argument ifst had an illegal value (ifst < 0 or ifst > n) = -8: The argument ilst had an illegal value (ilst < 0 or ilst > n)