1DORGTR(1)                LAPACK routine (version 3.2)                DORGTR(1)
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NAME

6       DORGTR  -  generates a real orthogonal matrix Q which is defined as the
7       product of n-1 elementary reflectors of order N, as returned by DSYTRD
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SYNOPSIS

10       SUBROUTINE DORGTR( 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           DOUBLE         PRECISION A( LDA, * ), TAU( * ), WORK( * )
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PURPOSE

19       DORGTR generates a real orthogonal matrix Q which  is  defined  as  the
20       product of n-1 elementary reflectors of order N, as returned by DSYTRD:
21       if UPLO = 'U', Q = H(n-1) . . . H(2) H(1),
22       if UPLO = 'L', Q = H(1) H(2) . . . H(n-1).
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ARGUMENTS

25       UPLO    (input) CHARACTER*1
26               = 'U': Upper triangle of A contains elementary reflectors  from
27               DSYTRD;  = 'L': Lower triangle of A contains elementary reflec‐
28               tors from DSYTRD.
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30       N       (input) INTEGER
31               The order of the matrix Q. N >= 0.
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33       A       (input/output) DOUBLE PRECISION array, dimension (LDA,N)
34               On entry, the vectors which define the  elementary  reflectors,
35               as  returned  by DSYTRD.  On exit, the N-by-N orthogonal matrix
36               Q.
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38       LDA     (input) INTEGER
39               The leading dimension of the array A. LDA >= max(1,N).
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41       TAU     (input) DOUBLE PRECISION array, dimension (N-1)
42               TAU(i) must contain the scalar factor of the elementary reflec‐
43               tor H(i), as returned by DSYTRD.
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45       WORK       (workspace/output)   DOUBLE   PRECISION   array,   dimension
46       (MAX(1,LWORK))
47               On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
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49       LWORK   (input) INTEGER
50               The dimension of the array  WORK.  LWORK  >=  max(1,N-1).   For
51               optimum  performance LWORK >= (N-1)*NB, where NB is the optimal
52               blocksize.  If LWORK = -1, then a workspace query  is  assumed;
53               the routine only calculates the optimal size of the WORK array,
54               returns this value as the first entry of the WORK array, and no
55               error message related to LWORK is issued by XERBLA.
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57       INFO    (output) INTEGER
58               = 0:  successful exit
59               < 0:  if INFO = -i, the i-th argument had an illegal value
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63 LAPACK routine (version 3.2)    November 2008                       DORGTR(1)
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