--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/scripts/control/system/sysdisc.m	Fri Jan 14 03:50:02 2000 +0000
@@ -0,0 +1,98 @@
+## 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{dsys}, @var{Adc}, @var{Cdc}] =} sysdisc (@var{sys})
+##
+## @strong{Inputs}
+## @var{sys} = system data structure
+##
+## @strong{Outputs}
+## @table @var
+## @item dsys
+## purely discrete portion of sys (returned empty if there is
+## no purely discrete path from inputs to outputs)
+## @item    Adc
+## @itemx   Cdc
+## connections from continuous states to discrete states and discrete
+## outputs, respectively.
+## @end table
+## @end deftypefn
+
+function [dsys, Adc, Cdc] = sysdisc (sys)
+
+  save_empty = empty_list_elements_ok;
+  empty_list_elements_ok = 1;
+
+  if (nargin != 1)
+    usage("[dsys,Adc,Cdc] = sysdisc(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
+  Add = Adc = Bdd = Cdd = Cdc = Ddd = [];
+
+  if(isempty(st_d) & isempty(y_d))
+    error("sysdisc: expecting discrete states and/or continous outputs");
+  elseif (isempty(st_d))
+    warning("sysdisc: no discrete states");
+  elseif(isempty(y_d))
+    warning("sysdisc: no discrete outputs");
+  endif
+
+  [aa,bb,cc,dd] = sys2ss(sys);
+  if(!isempty(st_d) )
+    Add = aa( st_d , st_d);
+    stname = sysgetsignals(sys,"st",st_d);
+    Bdd = bb( st_d , :);
+    if(!isempty(st_c))
+      Adc = aa( st_d , st_c);
+    endif
+    if(!isempty(y_d))
+      Cdd = cc(y_d , st_d);
+    endif
+  else
+    stname = [];
+  endif
+  if(!isempty(y_d))
+    Ddd = dd(y_d , :);
+    outname = sysgetsignals(sys,"out",y_d);
+    if(!isempty(st_c))
+      Cdc = cc(y_d , st_c);
+    endif
+  else
+    outname=[];
+  endif
+  inname = sysgetsignals(sys,"in");
+  outlist = 1:rows(outname);
+
+  if(!isempty(outname))
+    tsam = sysgettsam(sys);
+    [nc,nz] = sysdimensions(sys);
+    dsys = ss2sys(Add,Bdd,Cdd,Ddd,tsam,0,nz,stname,inname,outname,outlist);
+  else
+    dsys=[];
+  endif
+
+  empty_list_elements_ok = save_empty;
+
+endfunction