1DORGTR(1)                LAPACK routine (version 3.1)                DORGTR(1)
2
3
4

NAME

6       DORGTR  - a real orthogonal matrix Q which is defined as the product of
7       n-1 elementary reflectors of order N, as returned by DSYTRD
8

SYNOPSIS

10       SUBROUTINE DORGTR( UPLO, N, A, LDA, TAU, WORK, LWORK, INFO )
11
12           CHARACTER      UPLO
13
14           INTEGER        INFO, LDA, LWORK, N
15
16           DOUBLE         PRECISION A( LDA, * ), TAU( * ), WORK( * )
17

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
22       if UPLO = 'U', Q = H(n-1) . . . H(2) H(1),
23
24       if UPLO = 'L', Q = H(1) H(2) . . . H(n-1).
25
26

ARGUMENTS

28       UPLO    (input) CHARACTER*1
29               =  'U': Upper triangle of A contains elementary reflectors from
30               DSYTRD; = 'L': Lower triangle of A contains elementary  reflec‐
31               tors from DSYTRD.
32
33       N       (input) INTEGER
34               The order of the matrix Q. N >= 0.
35
36       A       (input/output) DOUBLE PRECISION array, dimension (LDA,N)
37               On  entry,  the vectors which define the elementary reflectors,
38               as returned by DSYTRD.  On exit, the N-by-N  orthogonal  matrix
39               Q.
40
41       LDA     (input) INTEGER
42               The leading dimension of the array A. LDA >= max(1,N).
43
44       TAU     (input) DOUBLE PRECISION array, dimension (N-1)
45               TAU(i) must contain the scalar factor of the elementary reflec‐
46               tor H(i), as returned by DSYTRD.
47
48       WORK      (workspace/output)   DOUBLE   PRECISION   array,    dimension
49       (MAX(1,LWORK))
50               On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
51
52       LWORK   (input) INTEGER
53               The  dimension  of  the  array  WORK. LWORK >= max(1,N-1).  For
54               optimum performance LWORK >= (N-1)*NB, where NB is the  optimal
55               blocksize.
56
57               If  LWORK  = -1, then a workspace query is assumed; the routine
58               only calculates the optimal size of  the  WORK  array,  returns
59               this  value  as the first entry of the WORK array, and no error
60               message related to LWORK is issued by XERBLA.
61
62       INFO    (output) INTEGER
63               = 0:  successful exit
64               < 0:  if INFO = -i, the i-th argument had an illegal value
65
66
67
68 LAPACK routine (version 3.1)    November 2006                       DORGTR(1)
Impressum