CUNGTR(l) ) CUNGTR(l)
CUNGTR - generate a complex unitary matrix Q which is defined as the product of n-1 ele-
mentary reflectors of order N, as returned by CHETRD
SUBROUTINE CUNGTR( UPLO, N, A, LDA, TAU, WORK, LWORK, INFO )
INTEGER INFO, LDA, LWORK, N
COMPLEX A( LDA, * ), TAU( * ), WORK( * )
CUNGTR generates a complex unitary matrix Q which is defined as the product of n-1 elemen-
tary reflectors of order N, as returned by CHETRD: 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 CHETRD; = 'L':
Lower triangle of A contains elementary reflectors from CHETRD.
N (input) INTEGER
The order of the matrix Q. N >= 0.
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.
LDA (input) INTEGER
The leading dimension of the array A. LDA >= N.
TAU (input) COMPLEX array, dimension (N-1)
TAU(i) must contain the scalar factor of the elementary reflector H(i), as
returned by CHETRD.
WORK (workspace/output) COMPLEX 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 CUNGTR(l)