cunghr(3F)

NAME
     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( LWORK )

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 submatrix 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 elementary 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.

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