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+## 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, 59 Temple Place, Suite 330, Boston, MA 02111 USA.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {[@var{csys}, @var{Acd}, @var{Ccd}] =} syscont (@var{sys})
+## Extract the purely continuous subsystem of an input system.
+##
+## @strong{Inputs}
+## @var{sys} is a system data structure
+##
+## @strong{Outputs}
+## @table @var
+## @item csys
+## is the purely continuous input/output connections of @var{sys}
+## @item Acd
+## @itemx Ccd
+## connections from discrete states to continuous states,
+## discrete states to continuous outputs, respectively.
+##
+## returns @var{csys} empty if no continuous/continous path exists
+## @end table
+## @end deftypefn
+
+## Author: John Ingram <ingraje@eng.auburn.edu>
+## Created: August 1996
+
+function [csys, Acd, Ccd] = syscont (sys)
+
+  save_empty = empty_list_elements_ok;
+  empty_list_elements_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);
+
+  empty_list_elements_ok = save_empty;
+
+endfunction