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

6       DORGQR - an M-by-N real matrix Q with orthonormal columns,
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SYNOPSIS

9       SUBROUTINE DORGQR( M, N, K, A, LDA, TAU, WORK, LWORK, INFO )
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11           INTEGER        INFO, K, LDA, LWORK, M, N
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13           DOUBLE         PRECISION A( LDA, * ), TAU( * ), WORK( * )
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PURPOSE

16       DORGQR  generates  an  M-by-N  real  matrix Q with orthonormal columns,
17       which is defined as the first N columns of a product  of  K  elementary
18       reflectors of order M
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20             Q  =  H(1) H(2) . . . H(k)
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22       as returned by DGEQRF.
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ARGUMENTS

26       M       (input) INTEGER
27               The number of rows of the matrix Q. M >= 0.
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29       N       (input) INTEGER
30               The number of columns of the matrix Q. M >= N >= 0.
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32       K       (input) INTEGER
33               The  number  of elementary reflectors whose product defines the
34               matrix Q. N >= K >= 0.
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36       A       (input/output) DOUBLE PRECISION array, dimension (LDA,N)
37               On entry, the i-th column must contain the vector which defines
38               the  elementary  reflector H(i), for i = 1,2,...,k, as returned
39               by DGEQRF in the first k columns of its array argument  A.   On
40               exit, the M-by-N matrix Q.
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42       LDA     (input) INTEGER
43               The first dimension of the array A. LDA >= max(1,M).
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45       TAU     (input) DOUBLE PRECISION array, dimension (K)
46               TAU(i) must contain the scalar factor of the elementary reflec‐
47               tor H(i), as returned by DGEQRF.
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49       WORK      (workspace/output)   DOUBLE   PRECISION   array,    dimension
50       (MAX(1,LWORK))
51               On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
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53       LWORK   (input) INTEGER
54               The  dimension of the array WORK. LWORK >= max(1,N).  For opti‐
55               mum performance LWORK >= N*NB, where NB is the  optimal  block‐
56               size.
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58               If  LWORK  = -1, then a workspace query is assumed; the routine
59               only calculates the optimal size of  the  WORK  array,  returns
60               this  value  as the first entry of the WORK array, and no error
61               message related to LWORK is issued by XERBLA.
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63       INFO    (output) INTEGER
64               = 0:  successful exit
65               < 0:  if INFO = -i, the i-th argument has an illegal value
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69 LAPACK routine (version 3.1)    November 2006                       DORGQR(1)