SRC/ctrexc.f(3)

NAME
SRC/ctrexc.f

SYNOPSIS

  Functions/Subroutines
subroutine ctrexc (compq, n, t, ldt, q, ldq, ifst, ilst, info)
CTREXC

Function/Subroutine Documentation

  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

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
    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.
    !>          If N == 0 arguments ILST and IFST may be any value.
    !>

    T

    !>          T is COMPLEX 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 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 >= 1, and if
    !>          COMPQ = 'V', 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.

Definition at line 125 of file ctrexc.f.

Author

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