new file mode 100644
--- /dev/null
+++ b/scripts/control/sysadd.m
@@ -0,0 +1,97 @@
+# 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 sys = sysadd(Gsys,Hsys)
+# 
+# [sys] = sysadd(Gsys,Hsys)
+#
+#
+# returns transfer function sys = Gsys + Hsys
+#
+# Method: Gsys and Hsys are connected in parallel
+# The vector are connected to both systems; the outputs will be 
+# added.  The names given to the system will be the G systems names.
+#
+#                  ________
+#             ----|  Gsys  |---
+#        u   |    ----------  +|         
+#        -----                (_)----> y
+#            |     ________   +|
+#             ----|  Hsys  |---
+#                  --------
+
+# Written by John Ingram July 1996
+# $Revision: 1.2 $
+
+  save_val = implicit_str_to_num_ok;	# save for later
+  implicit_str_to_num_ok = 1;
+
+  if(nargin != 2)
+    usage("sysadd:  [sys] = sysysadd(Gsys,Hsys)");
+  endif
+
+  # check inputs
+  if(!is_struct(Gsys) | !is_struct(Hsys))
+    error("Both Gsys and Hsys must be in system data structure form");
+  endif
+
+  # check for compatibility
+  [n,nz,mg,pg] = sysdimensions(Gsys);
+  [n,nz,mh,ph] = sysdimensions(Hsys);
+  if(mg != mh)
+    error(sprintf("Gsys inputs(%d) != Hsys inputs (%d)",mg,mh));
+  elseif(pg != ph)
+    error(sprintf("Gsys outputs(%d) != Hsys outputs (%d)",pg,ph));
+  endif
+
+  [Gst, Gin, Gout, Gyd] = sysgetsignals(Gsys);
+  [Hst, Hin, Hout, Hyd] = sysgetsignals(Hsys);
+
+  # check for digital to continuous addition
+  if (Gyd != Hyd)
+    error("can not add a discrete output to a continuous output");
+  endif
+
+  if( (Gsys.sys(1) == 0) | (Hsys.sys(1) == 0) )
+    # see if adding  transfer functions with identical denominators
+    Gsys = sysupdate(Gsys,"tf");
+    Hsys = sysupdate(Hsys,"tf");
+    if(Hsys.den == Gsys.den)
+      sys = Gsys;
+      sys.sys(1) = 0;
+      sys.num = sys.num + Hsys.num;
+      return
+    endif
+  endif
+
+  # make sure in ss form
+  Gsys = sysupdate(Gsys,"ss");
+  Hsys = sysupdate(Hsys,"ss");
+
+  sys = sysgroup(Gsys,Hsys);
+
+  eyin = eye(mg);
+  eyout = eye(pg);
+
+
+  inname = Gin;
+  outname = Gout;
+
+  sys = sysscale(sys,[eyout eyout],[eyin;eyin],outname,inname);
+
+endfunction