CUNGTR  -  generate  a  complex  unitary matrix Q which is
       defined as the product of  n-1  elementary  reflectors  of
       order N, as returned by CHETRD


SYNOPSIS

       SUBROUTINE CUNGTR( UPLO, N, A, LDA, TAU, WORK, LWORK, INFO
                          )

           CHARACTER      UPLO

           INTEGER        INFO, LDA, LWORK, N

           COMPLEX        A( LDA, * ), TAU( * ), WORK( * )


PURPOSE

       CUNGTR generates a  complex  unitary  matrix  Q  which  is
       defined  as  the  product  of n-1 elementary reflectors of
       order N, as returned by CHETRD: 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 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 ele­
               mentary 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.

               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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