DGERQ2(l) ) DGERQ2(l)
DGERQ2 - compute an RQ factorization of a real m by n matrix A
SUBROUTINE DGERQ2( M, N, A, LDA, TAU, WORK, INFO )
INTEGER INFO, LDA, M, N
DOUBLE PRECISION A( LDA, * ), TAU( * ), WORK( * )
DGERQ2 computes an RQ factorization of a real m by n matrix A: A = R * Q.
M (input) INTEGER
The number of rows of the matrix A. M >= 0.
N (input) INTEGER
The number of columns of the matrix A. N >= 0.
A (input/output) DOUBLE PRECISION array, dimension (LDA,N)
On entry, the m by n matrix A. On exit, if m <= n, the upper triangle of the sub-
array A(1:m,n-m+1:n) contains the m by m upper triangular matrix R; if m >= n, the
elements on and above the (m-n)-th subdiagonal contain the m by n upper trape-
zoidal matrix R; the remaining elements, with the array TAU, represent the orthog-
onal matrix Q as a product of elementary reflectors (see Further Details).
LDA (input) INTEGER
The leading dimension of the array A. LDA >= max(1,M).
TAU (output) DOUBLE PRECISION array, dimension (min(M,N))
The scalar factors of the elementary reflectors (see Further Details).
WORK (workspace) DOUBLE PRECISION array, dimension (M)
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value
The matrix Q is represented as a product of elementary reflectors
Q = H(1) H(2) . . . H(k), where k = min(m,n).
Each H(i) has the form
H(i) = I - tau * v * v'
where tau is a real scalar, and v is a real vector with
v(n-k+i+1:n) = 0 and v(n-k+i) = 1; v(1:n-k+i-1) is stored on exit in A(m-k+i,1:n-k+i-1),
and tau in TAU(i).
LAPACK version 3.0 15 June 2000 DGERQ2(l)