1DGEQR2(1)                LAPACK routine (version 3.2)                DGEQR2(1)
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NAME

6       DGEQR2 - computes a QR factorization of a real m by n matrix A
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SYNOPSIS

9       SUBROUTINE DGEQR2( 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       DGEQR2  computes  a QR factorization of a real m by n matrix A: A = Q *
17       R.
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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, the  elements  on  and
28               above the diagonal of the array contain the min(m,n) by n upper
29               trapezoidal matrix R (R is upper triangular if  m  >=  n);  the
30               elements  below the diagonal, with the array TAU, represent the
31               orthogonal matrix Q as a product of elementary reflectors  (see
32               Further  Details).   LDA     (input) INTEGER The leading dimen‐
33               sion of the array A.  LDA >= max(1,M).
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35       TAU     (output) DOUBLE PRECISION array, dimension (min(M,N))
36               The scalar factors of the elementary  reflectors  (see  Further
37               Details).
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39       WORK    (workspace) DOUBLE PRECISION array, dimension (N)
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41       INFO    (output) INTEGER
42               = 0: successful exit
43               < 0: if INFO = -i, the i-th argument had an illegal value
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FURTHER DETAILS

46       The matrix Q is represented as a product of elementary reflectors
47          Q = H(1) H(2) . . . H(k), where k = min(m,n).
48       Each H(i) has the form
49          H(i) = I - tau * v * v'
50       where tau is a real scalar, and v is a real vector with
51       v(1:i-1)  =  0  and v(i) = 1; v(i+1:m) is stored on exit in A(i+1:m,i),
52       and tau in TAU(i).
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56 LAPACK routine (version 3.2)    November 2008                       DGEQR2(1)