SGEQR2(1) LAPACK routine (version 3.2) SGEQR2(1)NAME
SGEQR2 - computes a QR factorization of a real m by n matrix A
SYNOPSIS
SUBROUTINE SGEQR2( M, N, A, LDA, TAU, WORK, INFO )
INTEGER INFO, LDA, M, N
REAL A( LDA, * ), TAU( * ), WORK( * )
PURPOSE
SGEQR2 computes a QR factorization of a real m by n matrix A: A = Q *
R.
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
above the diagonal of the array contain the min(m,n) by n upper
trapezoidal matrix R (R is upper triangular if m >= n); the
elements below 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 dimen‐
sion 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 (N)
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(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(1:i-1) = 0 and v(i) = 1; v(i+1:m) is stored on exit in A(i+1:m,i),
and tau in TAU(i).
LAPACK routine (version 3.2) November 2008 SGEQR2(1)
