# Copyright (C) 1996 Auburn University.  All Rights Reserved.
#
# This file is part of Octave. 
#
# Octave is free software; you can redistribute it and/or modify it 
# under the terms of the GNU General Public License as published by the 
# Free Software Foundation; either version 2, or (at your option) any 
# later version. 
# 
# Octave is distributed in the hope that it will be useful, but WITHOUT 
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 
# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License 
# for more details.
# 
# You should have received a copy of the GNU General Public License 
# along with Octave; see the file COPYING.  If not, write to the Free 
# Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. 
 
function [csys,Acd,Ccd] = syscont(sys)
# function [csys,Acd,Ccd] = syscont(sys)
# returns csys = sys with discrete states./utputs omitted.
#
# inputs: sys is a system data structure
# outputs: csys is the purely continuous input/output connections of
#               sys
#          Acd, Ccd: connections from discrete states to continuous states,
#               discrete states to continuous outputs, respectively.
#
# returns csys empty if no continuous/continous path exists

# Written by John Ingram August 1996

  save_val = implicit_str_to_num_ok;	# save for later
  save_empty = empty_list_elements_ok;
  empty_list_elements_ok = implicit_str_to_num_ok = 1;

  if (nargin != 1)
    usage("[csys,Acd,Ccd,Dcd] = syscont(sys)");
  elseif (!is_struct(sys))
    error("sys must be in system data structure form");
  endif

  sys = sysupdate(sys,"ss");
  [n_tot,st_c,st_d,y_c,y_d] = syscont_disc(sys);	# get ranges

  # assume there's nothing there; build partitions as appropriate
  Acc = Acd = Bcc = Ccc = Ccd = Dcc = [];

  if(isempty(st_c) & isempty(y_c))
    error("syscont: expecting continous states and/or continous outputs");
  elseif (isempty(st_c))
    warning("syscont: no continuous states");
  elseif(isempty(y_c))
    warning("syscont: no continuous outputs");
  endif

  [sys_a, sys_b, sys_c, sys_d ] = sys2ss(sys);
  [sys_stname, sys_inname, sys_outname] = sysgetsignals(sys);
  [sys_n, sys_nz, sys_m, sys_p] = sysdimensions(sys);
  if(!isempty(st_c))
    Acc = sys_a(st_c,st_c);
    stname = sys_stname(st_c);
    Bcc = sys_b(st_c,:);
    Ccc = sys_c(y_c,st_c);
    Acd = sys_a(st_c,st_d);
  else
    stname=[];
  endif
  outname = sys_outname(y_c);
  Dcc = sys_d(y_c,:);
  Ccd = sys_c(y_c,st_d);
  inname = sys_inname;
  
  csys = ss2sys(Acc,Bcc,Ccc,Dcc,0,sys_n,0,stname,inname,outname);

  implicit_str_to_num_ok = save_val;	# restore value
  empty_list_elements_ok = save_empty;
 
endfunction