CUNGQR - generate an M-by-N complex matrix Q with
orthonormal 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 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 CGEQRF.
WORK (workspace/output) COMPLEX array, dimension
(LWORK)
On exit, if INFO = 0, WORK(1) returns the optimal
LWORK.
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
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