zgeql2(3)

NAME

ZGEQL2 - compute a QL factorization of a complex m by n

matrix A

SYNOPSIS

SUBROUTINE ZGEQL2( M, N, A, LDA, TAU, WORK, INFO )
    INTEGER        INFO, LDA, M, N
    COMPLEX*16     A( LDA, * ), TAU( * ), WORK( * )

PURPOSE

ZGEQL2 computes a QL factorization of a complex m by n ma

trix A: A = Q * L.

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) COMPLEX*16 array, dimension (LDA,N)

On entry, the m by n matrix A. On exit, if m >=

n, the lower triangle of the subarray A(m-n+1:m,1:n) contains the

n by n lower triangular matrix L; if m <= n, the elements on and

below the (n-m)-th superdiagonal contain the m by n lower trape

zoidal matrix L; the remaining elements, with the array TAU, rep

resent the unitary matrix Q as a product of elementary reflectors

(see Further Details). LDA (input) INTEGER The leading di

mension of the array A. LDA >= max(1,M).

TAU (output) COMPLEX*16 array, dimension (min(M,N))

The scalar factors of the elementary reflectors

(see Further Details).

WORK (workspace) COMPLEX*16 array, dimension (N)

INFO (output) INTEGER

= 0: successful exit
< 0: if INFO = -i, the i-th argument had an ille

gal value

FURTHER DETAILS

The matrix Q is represented as a product of elementary re

flectors

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(m-k+i+1:m) = 0 and v(m-k+i) = 1; v(1:m-k+i-1) is stored on

exit in A(1:m-k+i-1,n-k+i), and tau in TAU(i).

LAPACK version 3.0 15 June 2000

ZGEQL2(3)