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+++ b/scripts/control/sysdup.m
@@ -0,0 +1,136 @@
+# 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 retsys = sysdup(Asys,output_list,input_list)
+# function retsys = sysdup(Asys,output_list,input_list)
+# Duplicate specified input/output connections of a system
+# 
+#
+# inputs:
+#   Asys: system data structure (see ss2sys)
+#   output_list,input_list: list of connections indices; 
+#       duplicates are made of y(output_list(ii)) and u(input_list(ii)).
+# output: retsys: resulting closed loop system:
+#    duplicated i/o names are appended with a "+" suffix.
+#
+# Operation: sysdup creates copies of selected inputs and outputs as
+# shown below.  u1/y1 is the set of original inputs/outputs, and 
+# u2,y2 is the set of duplicated inputs/outputs in the order specified
+# in input_list,output_list, respectively
+#                      ____________________
+#                      |                  |
+#     u1         ----->|                  |----> y1
+#                      |       Asys       |
+#                      |                  |
+#     u2 ------------->|                  |----->y2 
+#     (input_list)     |                  |      (output_list)
+#                      --------------------     
+
+# A. S. Hodel August 1995
+# modified 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 != 3)
+    usage("retsys = sysdup(Asys,output_list,input_list)");
+  endif
+
+  if( !is_struct(Asys))
+    error("Asys must be a system data structure (see ss2sys, tf2sys, or zp2sys)")
+  endif
+
+  if (Asys.sys(4) != 1)
+    Asys = sysupdate(Asys,'ss');
+  endif
+
+  mm = rows(Asys.inname);
+  pp = rows(Asys.outname);
+
+  # first duplicate inputs
+  if(is_vector(input_list))
+    for ii=1:length(input_list);
+      Asys.b(:,mm+ii) = Asys.b(:,input_list(ii));
+      Asys.d(:,mm+ii) = Asys.d(:,input_list(ii));
+    end
+  elseif(!isempty(input_list))
+    error("input_list must be a vector or empty");
+  endif
+
+
+  # now duplicate outputs
+  osize = min(size(output_list));
+  if(osize == 1)
+    for ii=1:length(output_list);
+      Asys.c(pp+ii,:) = Asys.c(output_list(ii),:);
+      Asys.d(pp+ii,:) = Asys.d(output_list(ii),:);
+    end
+  elseif(osize != 0)
+    error("output_list must be a vector or empty");
+  endif
+  
+  yd = Asys.yd(output_list);
+  Asys.yd = [Asys.yd yd];
+
+  # give default names to the added inputs
+  for ii=(mm+1):(mm+length(input_list))
+    orig_name = Asys.inname(input_list(ii-mm),:);
+
+    #disp("sysdup: orig_name=")
+    #orig_name
+    #disp("/sysdup")
+
+    strval = [dezero(orig_name),"(dup)"];
+     
+    #disp("sysdup: strval=")
+    #strval
+    #disp("/sysdup")
+
+    Asys.inname(ii,1:length(strval)) = [strval];
+     
+    #disp("sysdup: resulting Asys.inname:")
+    #Asys.inname
+    #disp("/sysdup");
+
+  endfor
+
+  # give default names to the added outputs
+  for jj=(pp+1):(pp+length(output_list))
+    if(isstr(Asys.outname))
+      orig_name =Asys.outname;
+    else
+      orig_name = Asys.outname(output_list(jj-pp),:);
+    endif
+    strval = [dezero(orig_name),"(dup)"];
+    Asys.outname(jj,1:length(strval)) = [strval];
+
+  endfor
+
+    
+
+  if(max(size(Asys.d)) > 1 )
+    Asys.sys = [2 0 0 1];	# change default form to state space
+				# tf and zp are no longer relevant
+  endif
+
+  retsys = Asys;
+
+  implicit_str_to_num_ok = save_val;	# restore value
+
+endfunction