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NAME ZTREXC - reorder 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 SYNOPSIS SUBROUTINE ZTREXC( COMPQ, N, T, LDT, Q, LDQ, IFST, ILST, INFO ) CHARACTER COMPQ INTEGER IFST, ILST, INFO, LDQ, LDT, N COMPLEX*16 Q( LDQ, * ), T( LDT, * ) PURPOSE ZTREXC 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. ARGUMENTS COMPQ (input) CHARACTER*1 = 'V': update the matrix Q of Schur vectors; = 'N': do not update Q. N (input) INTEGER The order of the matrix T. N >= 0. T (input/output) COMPLEX*16 array, dimension (LDT,N) On entry, the upper triangular matrix T. On exit, the reordered upper triangular matrix. LDT (input) INTEGER The leading dimension of the array T. LDT >= max(1,N). Q (input/output) COMPLEX*16 array, dimension (LDQ,N) On entry, if COMPQ = 'V', the matrix Q of Schur vec- tors. On exit, if COMPQ = 'V', Q has been postmul- tiplied by the unitary transformation matrix Z which reorders T. If COMPQ = 'N', Q is not referenced. LDQ (input) INTEGER The leading dimension of the array Q. LDQ >= max(1,N). IFST (input) INTEGER ILST (input) 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. INFO (output) INTEGER = 0: successful exit < 0: if INFO = -i, the i-th argument had an illegal value