ZUNGTR - generate a complex unitary matrix Q which is
defined as the product of n-1 elementary reflectors of
order N, as returned by ZHETRD
SYNOPSIS
SUBROUTINE ZUNGTR( UPLO, N, A, LDA, TAU, WORK, LWORK, INFO
)
CHARACTER UPLO
INTEGER INFO, LDA, LWORK, N
COMPLEX*16 A( LDA, * ), TAU( * ), WORK( * )
PURPOSE
ZUNGTR generates a complex unitary matrix Q which is
defined as the product of n-1 elementary reflectors of
order N, as returned by ZHETRD: if UPLO = 'U', Q = H(n-1)
. . . H(2) H(1),
if UPLO = 'L', Q = H(1) H(2) . . . H(n-1).
ARGUMENTS
UPLO (input) CHARACTER*1
= 'U': Upper triangle of A contains elementary
reflectors from ZHETRD; = 'L': Lower triangle of A
contains elementary reflectors from ZHETRD.
N (input) INTEGER
The order of the matrix Q. N >= 0.
A (input/output) COMPLEX*16 array, dimension (LDA,N)
On entry, the vectors which define the elementary
reflectors, as returned by ZHETRD. On exit, the
N-by-N unitary matrix Q.
LDA (input) INTEGER
The leading dimension of the array A. LDA >= N.
TAU (input) COMPLEX*16 array, dimension (N-1)
TAU(i) must contain the scalar factor of the ele
mentary reflector H(i), as returned by ZHETRD.
WORK (workspace/output) COMPLEX*16 array, dimension
(LWORK)
On exit, if INFO = 0, WORK(1) returns the optimal
LWORK.
LWORK (input) INTEGER
The dimension of the array WORK. LWORK >= N-1.
For optimum performance LWORK >= (N-1)*NB, where
NB is the optimal blocksize.
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 had an ille
gal value
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