          form.
          On exit, if JOBU = 'I', then the leading N-by-N part of
          this array contains the matrix of accumulated unitary
          similarity transformations which reduces the given pair
          to observer Hessenberg form.
          If JOBU = 'N', the array U is not referenced and can be
          supplied as a dummy array (i.e. set parameter LDU = 1 and
          declare this array to be U(1,1) in the calling program).

  LDU     INTEGER
          The leading dimension of array 