SGELQF(l) LAPACK routine (version 1.1) SGELQF(l)
NAME
SGELQF - compute an LQ factorization of a real M-by-N matrix A
SYNOPSIS
SUBROUTINE SGELQF( M, N, A, LDA, TAU, WORK, LWORK, INFO )
INTEGER INFO, LDA, LWORK, M, N
REAL A( LDA, * ), TAU( * ), WORK( LWORK )
PURPOSE
SGELQF computes an LQ factorization of a real M-by-N matrix A: A = L * Q.
ARGUMENTS
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) REAL array, dimension (LDA,N)
On entry, the M-by-N matrix A. On exit, the elements on and below
the diagonal of the array contain the m-by-min(m,n) lower tra-
pezoidal matrix L (L is lower triangular if m <= n); the elements
above the diagonal, with the array TAU, represent the orthogonal
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) REAL array, dimension (min(M,N))
The scalar factors of the elementary reflectors (see Further
Details).
WORK (workspace) REAL array, dimension (LWORK)
On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
LWORK (input) INTEGER
The dimension of the array WORK. LWORK >= max(1,M). For optimum
performance LWORK >= M*NB, where NB is the optimal blocksize.
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value
FURTHER DETAILS
The matrix Q is represented as a product of elementary reflectors
Q = H(k) . . . H(2) H(1), 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(1:i-1) = 0 and v(i) = 1; v(i+1:n) is stored on exit in A(i,i+1:n), and
tau in TAU(i).
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value decomposition