1DGERQ2(1)                LAPACK routine (version 3.2)                DGERQ2(1)
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NAME

6       DGERQ2 - computes an RQ factorization of a real m by n matrix A
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SYNOPSIS

9       SUBROUTINE DGERQ2( M, N, A, LDA, TAU, WORK, INFO )
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11           INTEGER        INFO, LDA, M, N
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13           DOUBLE         PRECISION A( LDA, * ), TAU( * ), WORK( * )
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PURPOSE

16       DGERQ2  computes an RQ factorization of a real m by n matrix A: A = R *
17       Q.
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ARGUMENTS

20       M       (input) INTEGER
21               The number of rows of the matrix A.  M >= 0.
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23       N       (input) INTEGER
24               The number of columns of the matrix A.  N >= 0.
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26       A       (input/output) DOUBLE PRECISION array, dimension (LDA,N)
27               On entry, the m by n matrix A.  On exit, if m <= n,  the  upper
28               triangle  of  the  subarray  A(1:m,n-m+1:n) contains the m by m
29               upper triangular matrix R; if m >= n, the elements on and above
30               the  (m-n)-th  subdiagonal contain the m by n upper trapezoidal
31               matrix R; the remaining elements, with the array TAU, represent
32               the  orthogonal  matrix Q as a product of elementary reflectors
33               (see Further Details).
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35       LDA     (input) INTEGER
36               The leading dimension of the array A.  LDA >= max(1,M).
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38       TAU     (output) DOUBLE PRECISION array, dimension (min(M,N))
39               The scalar factors of the elementary  reflectors  (see  Further
40               Details).
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42       WORK    (workspace) DOUBLE PRECISION array, dimension (M)
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44       INFO    (output) INTEGER
45               = 0: successful exit
46               < 0: if INFO = -i, the i-th argument had an illegal value
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FURTHER DETAILS

49       The matrix Q is represented as a product of elementary reflectors
50          Q = H(1) H(2) . . . H(k), where k = min(m,n).
51       Each H(i) has the form
52          H(i) = I - tau * v * v'
53       where tau is a real scalar, and v is a real vector with
54       v(n-k+i+1:n)  =  0  and v(n-k+i) = 1; v(1:n-k+i-1) is stored on exit in
55       A(m-k+i,1:n-k+i-1), and tau in TAU(i).
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59 LAPACK routine (version 3.2)    November 2008                       DGERQ2(1)