- SUBROUTINE CGELQ2(
- M, N, A, LDA, TAU, WORK, INFO )
- INTEGER INFO, LDA, M, N
- COMPLEX A( LDA, * ), TAU( * ), WORK( * )
PURPOSECGELQ2 computes an LQ factorization of a complex m by n matrix A: A = L * 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) COMPLEX 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 trapezoidal matrix L (L is lower triangular if m <= n); the elements above the diagonal, with the array TAU, represent the unitary 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) COMPLEX array, dimension (min(M,N))
- The scalar factors of the elementary reflectors (see Further Details).
- WORK (workspace) COMPLEX array, dimension (M)
- INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value
FURTHER DETAILSThe 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 complex scalar, and v is a complex vector with v(1:i-1) = 0 and v(i) = 1; conjg(v(i+1:n)) is stored on exit in A(i,i+1:n), and tau in TAU(i).