CUNGHR - generate a complex unitary matrix Q which is
defined as the product of IHI-ILO elementary reflectors of
order N, as returned by CGEHRD
SYNOPSIS
SUBROUTINE CUNGHR( N, ILO, IHI, A, LDA, TAU, WORK, LWORK,
INFO )
INTEGER IHI, ILO, INFO, LDA, LWORK, N
COMPLEX A( LDA, * ), TAU( * ), WORK( * )
PURPOSE
CUNGHR generates a complex unitary matrix Q which is
defined as the product of IHI-ILO elementary reflectors of
order N, as returned by CGEHRD: Q = H(ilo) H(ilo+1) . . .
H(ihi-1).
ARGUMENTS
N (input) INTEGER
The order of the matrix Q. N >= 0.
ILO (input) INTEGER
IHI (input) INTEGER ILO and IHI must have the
same values as in the previous call of CGEHRD. Q
is equal to the unit matrix except in the subma
trix Q(ilo+1:ihi,ilo+1:ihi). 1 <= ILO <= IHI <=
N, if N > 0; ILO=1 and IHI=0, if N=0.
A (input/output) COMPLEX array, dimension (LDA,N)
On entry, the vectors which define the elementary
reflectors, as returned by CGEHRD. On exit, the
N-by-N unitary matrix Q.
LDA (input) INTEGER
The leading dimension of the array A. LDA >=
max(1,N).
TAU (input) COMPLEX array, dimension (N-1)
TAU(i) must contain the scalar factor of the ele
mentary reflector H(i), as returned by CGEHRD.
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 >= IHI-ILO.
For optimum performance LWORK >= (IHI-ILO)*NB,
where NB is the optimal blocksize.
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 ille
gal value
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