.TH CUNGTR 1 "November 2006" " LAPACK routine (version 3.1) " " LAPACK routine (version 3.1) "
.SH NAME
CUNGTR - a complex unitary matrix Q which is defined as the product of n-1 elementary reflectors of order N, as returned by CHETRD
.SH SYNOPSIS
.TP 19
SUBROUTINE CUNGTR(
UPLO, N, A, LDA, TAU, WORK, LWORK, INFO )
.TP 19
.ti +4
CHARACTER
UPLO
.TP 19
.ti +4
INTEGER
INFO, LDA, LWORK, N
.TP 19
.ti +4
COMPLEX
A( LDA, * ), TAU( * ), WORK( * )
.SH PURPOSE
CUNGTR generates a complex unitary matrix Q which is defined as the
product of n-1 elementary reflectors of order N, as returned by
CHETRD:
if UPLO = \(aqU\(aq, Q = H(n-1) . . . H(2) H(1),
.br
if UPLO = \(aqL\(aq, Q = H(1) H(2) . . . H(n-1).
.br
.SH ARGUMENTS
.TP 8
UPLO (input) CHARACTER*1
= \(aqU\(aq: Upper triangle of A contains elementary reflectors
from CHETRD;
= \(aqL\(aq: Lower triangle of A contains elementary reflectors
from CHETRD.
.TP 8
N (input) INTEGER
The order of the matrix Q. N >= 0.
.TP 8
A (input/output) COMPLEX array, dimension (LDA,N)
On entry, the vectors which define the elementary reflectors,
as returned by CHETRD.
On exit, the N-by-N unitary matrix Q.
.TP 8
LDA (input) INTEGER
The leading dimension of the array A. LDA >= N.
.TP 8
TAU (input) COMPLEX array, dimension (N-1)
TAU(i) must contain the scalar factor of the elementary
reflector H(i), as returned by CHETRD.
.TP 8
WORK (workspace/output) COMPLEX array, dimension (MAX(1,LWORK))
On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
.TP 8
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.
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.
.TP 8
INFO (output) INTEGER
= 0: successful exit
.br
< 0: if INFO = -i, the i-th argument had an illegal value