1CTREXC(1)                LAPACK routine (version 3.1)                CTREXC(1)
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NAME

6       CTREXC  -  the Schur factorization of a complex matrix A = Q*T*Q**H, so
7       that the diagonal element of T with row index IFST is moved to row ILST
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SYNOPSIS

10       SUBROUTINE CTREXC( COMPQ, N, T, LDT, Q, LDQ, IFST, ILST, INFO )
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12           CHARACTER      COMPQ
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14           INTEGER        IFST, ILST, INFO, LDQ, LDT, N
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16           COMPLEX        Q( LDQ, * ), T( LDT, * )
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PURPOSE

19       CTREXC reorders the  Schur  factorization  of  a  complex  matrix  A  =
20       Q*T*Q**H,  so  that  the  diagonal  element of T with row index IFST is
21       moved to row ILST.
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23       The Schur form T is reordered by a  unitary  similarity  transformation
24       Z**H*T*Z,  and  optionally  the matrix Q of Schur vectors is updated by
25       postmultplying it with Z.
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ARGUMENTS

29       COMPQ   (input) CHARACTER*1
30               = 'V':  update the matrix Q of Schur vectors;
31               = 'N':  do not update Q.
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33       N       (input) INTEGER
34               The order of the matrix T. N >= 0.
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36       T       (input/output) COMPLEX array, dimension (LDT,N)
37               On  entry,  the  upper  triangular  matrix  T.   On  exit,  the
38               reordered upper triangular matrix.
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40       LDT     (input) INTEGER
41               The leading dimension of the array T. LDT >= max(1,N).
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43       Q       (input/output) COMPLEX array, dimension (LDQ,N)
44               On  entry,  if  COMPQ = 'V', the matrix Q of Schur vectors.  On
45               exit, if COMPQ = 'V', Q has been postmultiplied by the  unitary
46               transformation matrix Z which reorders T.  If COMPQ = 'N', Q is
47               not referenced.
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49       LDQ     (input) INTEGER
50               The leading dimension of the array Q.  LDQ >= max(1,N).
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52       IFST    (input) INTEGER
53               ILST    (input) INTEGER Specify the reordering of the  diagonal
54               elements  of T: The element with row index IFST is moved to row
55               ILST by a sequence of transpositions between adjacent elements.
56               1 <= IFST <= N; 1 <= ILST <= N.
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58       INFO    (output) INTEGER
59               = 0:  successful exit
60               < 0:  if INFO = -i, the i-th argument had an illegal value
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64 LAPACK routine (version 3.1)    November 2006                       CTREXC(1)