.TH ZTREXC 1 "November 2006" " LAPACK routine (version 3.1) " " LAPACK routine (version 3.1) " .SH NAME ZTREXC - 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 .SH SYNOPSIS .TP 19 SUBROUTINE ZTREXC( COMPQ, N, T, LDT, Q, LDQ, IFST, ILST, INFO ) .TP 19 .ti +4 CHARACTER COMPQ .TP 19 .ti +4 INTEGER IFST, ILST, INFO, LDQ, LDT, N .TP 19 .ti +4 COMPLEX*16 Q( LDQ, * ), T( LDT, * ) .SH 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 postmultplying it with Z. .br .SH ARGUMENTS .TP 8 COMPQ (input) CHARACTER*1 = \(aqV\(aq: update the matrix Q of Schur vectors; .br = \(aqN\(aq: do not update Q. .TP 8 N (input) INTEGER The order of the matrix T. N >= 0. .TP 8 T (input/output) COMPLEX*16 array, dimension (LDT,N) On entry, the upper triangular matrix T. On exit, the reordered upper triangular matrix. .TP 8 LDT (input) INTEGER The leading dimension of the array T. LDT >= max(1,N). .TP 8 Q (input/output) COMPLEX*16 array, dimension (LDQ,N) On entry, if COMPQ = \(aqV\(aq, the matrix Q of Schur vectors. On exit, if COMPQ = \(aqV\(aq, Q has been postmultiplied by the unitary transformation matrix Z which reorders T. If COMPQ = \(aqN\(aq, Q is not referenced. .TP 8 LDQ (input) INTEGER The leading dimension of the array Q. LDQ >= max(1,N). .TP 8 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. .TP 8 INFO (output) INTEGER = 0: successful exit .br < 0: if INFO = -i, the i-th argument had an illegal value