cungql(3)

NAME

CUNGQL - generate an M-by-N complex matrix Q with or

thonormal columns,

SYNOPSIS

SUBROUTINE CUNGQL( M, N, K, A, LDA, TAU, WORK, LWORK, INFO
)
    INTEGER        INFO, K, LDA, LWORK, M, N
    COMPLEX        A( LDA, * ), TAU( * ), WORK( * )

PURPOSE

CUNGQL generates an M-by-N complex matrix Q with orthonor

mal columns, which is defined as the last N columns of a product

of K elementary reflectors of order M

Q = H(k) . . . H(2) H(1)

as returned by CGEQLF.

ARGUMENTS

M (input) INTEGER

The number of rows of the matrix Q. M >= 0.

N (input) INTEGER

The number of columns of the matrix Q. M >= N >=

0.

K (input) INTEGER

The number of elementary reflectors whose product

defines the matrix Q. N >= K >= 0.

A (input/output) COMPLEX array, dimension (LDA,N)

On entry, the (n-k+i)-th column must contain the

vector which defines the elementary reflector H(i), for i =

1,2,...,k, as returned by CGEQLF in the last k columns of its ar

ray argument A. On exit, the M-by-N matrix Q.

LDA (input) INTEGER

The first dimension of the array A. LDA >=

max(1,M).

TAU (input) COMPLEX array, dimension (K)

TAU(i) must contain the scalar factor of the ele

mentary reflector H(i), as returned by CGEQLF.

WORK (workspace/output) COMPLEX 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,N). For optimum performance LWORK >= N*NB, where NB is the

optimal blocksize.

If LWORK = -1, then a workspace query is assumed;

the routine only calculates the optimal size of the WORK array,

returns this value as the first entry of the WORK array, and no

error message related to LWORK is issued by XERBLA.

INFO (output) INTEGER

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

gal value

LAPACK version 3.0 15 June 2000

CUNGQL(3)