# Copyright (C) 1996,1998 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. 
 
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

  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

  Asys = sysupdate(Asys,"ss");
  [nn,nz,mm,pp] = sysdimensions(Asys);
  [aa,bb,cc,dd] = sys2ss(Asys);

  # first duplicate inputs
  if(is_vector(input_list))
    for ii=1:length(input_list);
      bb(:,mm+ii) = bb(:,input_list(ii));
      dd(:,mm+ii) = dd(:,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);
      cc(pp+ii,:) = cc(output_list(ii),:);
      dd(pp+ii,:) = dd(output_list(ii),:);
    end
  elseif(osize != 0)
    error("output_list must be a vector or empty");
  endif
  
  [stnam,innam,outnam,yd] = sysgetsignals(Asys);
  tsam = sysgettsam(Asys);

  # pack system and then rename signals
  retsys = ss2sys(aa,bb,cc,dd,tsam,nn,nz);
  retsys = syssetsignals(retsys,"in",innam,1:mm);
  retsys = syssetsignals(retsys,"out",outnam,1:pp);
  retsys = syssetsignals(retsys,"yd",yd,1:pp);

  # update added input names
  for ii=(mm+1):(mm+length(input_list))
    onum = input_list(ii-mm);
    strval = sprintf("%s(dup)",sysgetsignals(retsys,"in",onum,1) );
    retsys = syssetsignals(retsys,"in",strval,ii);
  endfor

  # update added output names/discrete flags
  # give default names to the added outputs
  for jj=(pp+1):(pp+length(output_list))
    onum = output_list(jj-pp);
    strval = sprintf("%s(dup)",sysgetsignals(retsys,"out",onum,1) );
    retsys = syssetsignals(retsys,"out",strval,jj);
    dflg = sysgetsignals(retsys,"yd",onum);
    retsys = syssetsignals(retsys,"yd",dflg,jj);
  endfor

  implicit_str_to_num_ok = save_val;	# restore value

endfunction