ZUNGTR(l) ) ZUNGTR(l)
ZUNGTR - generate a complex unitary matrix Q which is defined as the product of n-1 ele-
mentary reflectors of order N, as returned by ZHETRD
SUBROUTINE ZUNGTR( UPLO, N, A, LDA, TAU, WORK, LWORK, INFO )
INTEGER INFO, LDA, LWORK, N
COMPLEX*16 A( LDA, * ), TAU( * ), WORK( * )
ZUNGTR generates a complex unitary matrix Q which is defined as the product of n-1 elemen-
tary reflectors of order N, as returned by ZHETRD: if UPLO = 'U', Q = H(n-1) . . . H(2)
if UPLO = 'L', Q = H(1) H(2) . . . H(n-1).
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.
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 version 3.0 15 June 2000 ZUNGTR(l)