NAME

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( LWORK )

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 elementary 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.

INFO    (output) INTEGER
= 0:  successful exit
< 0:  if INFO = -i, the i-th argument had an illegal value

  —  LAPACK version 2.0  —  08 October 1994