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

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

10       SUBROUTINE SORGHR( N, ILO, IHI, A, LDA, TAU, WORK, LWORK, INFO )
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12           INTEGER        IHI, ILO, INFO, LDA, LWORK, N
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14           REAL           A( LDA, * ), TAU( * ), WORK( * )
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PURPOSE

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

25       N       (input) INTEGER
26               The order of the matrix Q. N >= 0.
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28       ILO     (input) INTEGER
29               IHI     (input) INTEGER ILO and IHI must have the  same  values
30               as  in  the  previous  call  of  SGEHRD. Q is equal to the unit
31               matrix except in the submatrix  Q(ilo+1:ihi,ilo+1:ihi).   1  <=
32               ILO <= IHI <= N, if N > 0; ILO=1 and IHI=0, if N=0.
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34       A       (input/output) REAL array, dimension (LDA,N)
35               On  entry,  the vectors which define the elementary reflectors,
36               as returned by SGEHRD.  On exit, the N-by-N  orthogonal  matrix
37               Q.
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39       LDA     (input) INTEGER
40               The leading dimension of the array A. LDA >= max(1,N).
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42       TAU     (input) REAL array, dimension (N-1)
43               TAU(i) must contain the scalar factor of the elementary reflec‐
44               tor H(i), as returned by SGEHRD.
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46       WORK    (workspace/output) REAL array, dimension (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 >= IHI-ILO.  For optimum
51               performance  LWORK  >=  (IHI-ILO)*NB,  where  NB is the optimal
52               blocksize.
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54               If LWORK = -1, then a workspace query is assumed;  the  routine
55               only  calculates  the  optimal  size of the WORK array, returns
56               this value as the first entry of the WORK array, and  no  error
57               message related to LWORK is issued by XERBLA.
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59       INFO    (output) INTEGER
60               = 0:  successful exit
61               < 0:  if INFO = -i, the i-th argument had an illegal value
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65 LAPACK routine (version 3.1)    November 2006                       SORGHR(1)