function [K_x T] = ppp_open2closed (A_u,A_c,k_x,x_0);
function [K_x T] = ppp_open2closed (A_u,A_c,k_x,x_0,Us0);

  ## usage:  [K_x T] = ppp_open2closed (A_u,A_c,k_x,x_0);
  ## usage:  [K_x T] = ppp_open2closed (A_u,A_c,k_x,x_0[,Us0]);
  ## K_x is the open-loop matrix as in U = K_w W - K_x x
  ## Note that K_x is a column vector of matrices - one matrix per input.
  ## T is the transformation matrix: x = T*Ustar; A_c = T*A_u*T^-1; U = (k_x*T)'
  ## A_u: The control basis-function matrix
  ## Us0: The initial value of Ustar
  ## A_c: closed-loop system matrix
  ## k_x: closed-loop feedback gain
  ## x_0: initial state
  ## Us0: initial basis fun state

  ## Copyright (C) 1999 by Peter J. Gawthrop
  ## 	$Id$	


  ## 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)
    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
    x_0 = zeros(n_c,1);
  endif

  ## Create U*(0)
  ##Us0  = ppp_ustar(A_u,n_u);
  Us0 = ones(1,n_o);
  if nargin<5 #Create U*(0)
    ##Us0  = ppp_ustar(A_u,n_u);
    Us0 = ones(1,n_o);
  endif
  

  ## Decompose A_u and Us0 into two bits:
  if n_o==n_c
    A_w = [];
    u_0 = Us0(1:n_c)';		# Assume same Us0 on each input
  else
    A_w = A_u(n_c+1:n_o, n_c+1:n_o)