NAME

       ztrexc.f -

SYNOPSIS

   Functions/Subroutines
       subroutine ztrexc (COMPQ, N, T, LDT, Q, LDQ, IFST, ILST, INFO)
           ZTREXC

Function/Subroutine Documentation

   subroutine ztrexc (character COMPQ, integer N, complex*16, dimension( ldt, * ) T, integer LDT,
       complex*16, dimension( ldq, * ) Q, integer LDQ, integer IFST, integer ILST, integer INFO)
       ZTREXC

       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.

       Parameters:
           COMPQ

                     COMPQ is CHARACTER*1
                     = 'V':  update the matrix Q of Schur vectors;
                     = 'N':  do not update Q.

           N

                     N is INTEGER
                     The order of the matrix T. N >= 0.

           T

                     T is COMPLEX*16 array, dimension (LDT,N)
                     On entry, the upper triangular matrix T.
                     On exit, the reordered upper triangular matrix.

           LDT

                     LDT is INTEGER
                     The leading dimension of the array T. LDT >= max(1,N).

           Q

                     Q is COMPLEX*16 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.

           LDQ

                     LDQ is INTEGER
                     The leading dimension of the array Q.  LDQ >= max(1,N).

           IFST

                     IFST is INTEGER

           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.

           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.

       Date:
           November 2011

Author

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