ZUNGTR(1) LAPACK routine (version 3.2) ZUNGTR(1)NAME
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
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 reflec‐
tors 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 elementary reflec‐
tor H(i), as returned by ZHETRD.
WORK (workspace/output) COMPLEX*16 array, dimension (MAX(1,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 block‐
size. 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 had an illegal value
LAPACK routine (version 3.2) November 2008 ZUNGTR(1)
