## 	$Id$	


  ## Check sizes
  n_o = is_square(A_u);
  n_c = is_square(A_c);

  if (n_o==0)||(n_c==0)||(n_o<>n_c)
  if (n_o==0)||(n_c==0)||(n_o!=n_c)
    error("A_u and A_c must be square and of the same dimension");
  endif

  [n_u,n_x] = size(k_x);

  ## Defaults
  if nargin<4