new file mode 100644
--- /dev/null
+++ b/scripts/control/sysdisc.m
@@ -0,0 +1,90 @@
+# Copyright (C) 1996 A. Scottedward Hodel 
+#
+# 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 [dsys,Adc,Cdc] = sysdisc(sys)
+# function [dsys,Adc,Cdc] = sysdisc(sys)
+# inputs: sys = system data structure
+# outputs:
+#    dsys: purely discrete portion of sys (returned empty if there is
+#          no purely discrete path from inputs to outputs)
+#    Adc, Cdc: connections from continuous states to discrete states/discrete
+#    outputs, respectively.
+#
+
+# $Revision: 1.1.1.1 $
+
+  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("[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
+
+  if(!isempty(st_d) )
+    Add = sys.a( st_d , st_d);
+    stname = sys.stname(st_d , :);
+    Bdd = sys.b( st_d , :);
+    if(!isempty(st_c))
+      Adc = sys.a( st_d , st_c);
+    endif
+    if(!isempty(y_d))
+      Cdd = sys.c(y_d , st_d);
+    endif
+  else
+    stname = [];
+  endif
+  if(!isempty(y_d))
+    Ddd = sys.d(y_d , :);
+    outname = sys.outname(y_d , :);
+    if(!isempty(st_c))
+      Cdc = sys.c(y_d , st_c);
+    endif
+  else
+    outname=[];
+  endif
+  inname = sys.inname;
+  outlist = 1:rows(outname);
+
+  if(!isempty(outname))
+    dsys = ss2sys(Add,Bdd,Cdd,Ddd,sys.tsam,0,sys.nz,stname, ...
+	inname,outname,outlist);
+  else
+    dsys=[];
+  endif
+  implicit_str_to_num_ok = save_val;	# restore value
+  empty_list_elements_ok = save_empty;
+
+endfunction