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

6       DORGHR  -  generates a real orthogonal matrix Q which is defined as the
7       product of IHI-ILO elementary reflectors of order  N,  as  returned  by
8       DGEHRD
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SYNOPSIS

11       SUBROUTINE DORGHR( N, ILO, IHI, A, LDA, TAU, WORK, LWORK, INFO )
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13           INTEGER        IHI, ILO, INFO, LDA, LWORK, N
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15           DOUBLE         PRECISION A( LDA, * ), TAU( * ), WORK( * )
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PURPOSE

18       DORGHR  generates  a  real  orthogonal matrix Q which is defined as the
19       product of IHI-ILO elementary reflectors of order  N,  as  returned  by
20       DGEHRD: Q = H(ilo) H(ilo+1) . . . H(ihi-1).
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ARGUMENTS

23       N       (input) INTEGER
24               The order of the matrix Q. N >= 0.
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26       ILO     (input) INTEGER
27               IHI      (input)  INTEGER ILO and IHI must have the same values
28               as in the previous call of DGEHRD.  Q  is  equal  to  the  unit
29               matrix  except  in  the submatrix Q(ilo+1:ihi,ilo+1:ihi).  1 <=
30               ILO <= IHI <= N, if N > 0; ILO=1 and IHI=0, if N=0.
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32       A       (input/output) DOUBLE PRECISION array, dimension (LDA,N)
33               On entry, the vectors which define the  elementary  reflectors,
34               as  returned  by DGEHRD.  On exit, the N-by-N orthogonal matrix
35               Q.
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37       LDA     (input) INTEGER
38               The leading dimension of the array A. LDA >= max(1,N).
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40       TAU     (input) DOUBLE PRECISION array, dimension (N-1)
41               TAU(i) must contain the scalar factor of the elementary reflec‐
42               tor H(i), as returned by DGEHRD.
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44       WORK       (workspace/output)   DOUBLE   PRECISION   array,   dimension
45       (MAX(1,LWORK))
46               On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
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48       LWORK   (input) INTEGER
49               The dimension of the array WORK. LWORK >= IHI-ILO.  For optimum
50               performance  LWORK  >=  (IHI-ILO)*NB,  where  NB is the optimal
51               blocksize.  If LWORK = -1, then a workspace query  is  assumed;
52               the routine only calculates the optimal size of the WORK array,
53               returns this value as the first entry of the WORK array, and no
54               error message related to LWORK is issued by XERBLA.
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56       INFO    (output) INTEGER
57               = 0:  successful exit
58               < 0:  if INFO = -i, the i-th argument had an illegal value
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62 LAPACK routine (version 3.2)    November 2008                       DORGHR(1)