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

6       CUNGTR  - a complex unitary matrix Q which is defined as the product of
7       n-1 elementary reflectors of order N, as returned by CHETRD
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SYNOPSIS

10       SUBROUTINE CUNGTR( UPLO, N, A, LDA, TAU, WORK, LWORK, INFO )
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12           CHARACTER      UPLO
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14           INTEGER        INFO, LDA, LWORK, N
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16           COMPLEX        A( LDA, * ), TAU( * ), WORK( * )
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PURPOSE

19       CUNGTR generates a complex unitary matrix Q which  is  defined  as  the
20       product of n-1 elementary reflectors of order N, as returned by CHETRD:
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22       if UPLO = 'U', Q = H(n-1) . . . H(2) H(1),
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24       if UPLO = 'L', Q = H(1) H(2) . . . H(n-1).
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ARGUMENTS

28       UPLO    (input) CHARACTER*1
29               =  'U': Upper triangle of A contains elementary reflectors from
30               CHETRD; = 'L': Lower triangle of A contains elementary  reflec‐
31               tors from CHETRD.
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33       N       (input) INTEGER
34               The order of the matrix Q. N >= 0.
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36       A       (input/output) COMPLEX array, dimension (LDA,N)
37               On  entry,  the vectors which define the elementary reflectors,
38               as returned by CHETRD.  On exit, the N-by-N unitary matrix Q.
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40       LDA     (input) INTEGER
41               The leading dimension of the array A. LDA >= N.
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43       TAU     (input) COMPLEX array, dimension (N-1)
44               TAU(i) must contain the scalar factor of the elementary reflec‐
45               tor H(i), as returned by CHETRD.
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47       WORK    (workspace/output) COMPLEX array, dimension (MAX(1,LWORK))
48               On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
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50       LWORK   (input) INTEGER
51               The  dimension  of  the  array WORK. LWORK >= N-1.  For optimum
52               performance LWORK >= (N-1)*NB, where NB is the  optimal  block‐
53               size.
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55               If  LWORK  = -1, then a workspace query is assumed; the routine
56               only calculates the optimal size of  the  WORK  array,  returns
57               this  value  as the first entry of the WORK array, and no error
58               message related to LWORK is issued by XERBLA.
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60       INFO    (output) INTEGER
61               = 0:  successful exit
62               < 0:  if INFO = -i, the i-th argument had an illegal value
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66 LAPACK routine (version 3.1)    November 2006                       CUNGTR(1)
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