cungqr(3)

NAME

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

thonormal columns,

SYNOPSIS

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

PURPOSE

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

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

of K elementary reflectors of order M

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

as returned by CGEQRF.

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 i-th column must contain the vector

which defines the elementary reflector H(i), for i = 1,2,...,k,

as returned by CGEQRF in the first k columns of its array argu

ment 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 CGEQRF.

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

CUNGQR(3)