--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/scripts/control/system/sysconnect.m	Fri Jan 14 03:50:02 2000 +0000
@@ -0,0 +1,277 @@
+## 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.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {@var{retsys} =} sysconnect (@var{sys}, @var{out_idx},@var{in_idx}@{,@var{order}, @var{tol}@})
+## Close the loop from specified outputs to respective specified inputs
+##
+## @strong{Inputs}
+## @table @var
+## @item   sys
+## system data structure
+## @item   out_idx
+## @itemx  in_idx
+## list of connections indices; @math{y(out_idx(ii))}
+## is connected to @math{u(in_idx(ii))}.
+## @item   order
+## logical flag (default = 0)
+## @table @code
+## @item        0
+## leave inputs and outputs in their original order
+## @item        1
+## permute inputs and outputs to the order shown in the diagram below
+## @end table
+## @item     tol
+## tolerance for singularities in algebraic loops default: 200@var{eps}
+## @end table
+##
+## @strong{Outputs}
+## @var{sys}: resulting closed loop system.
+##
+## @strong{Method}
+## @code{sysconnect} internally permutes selected inputs, outputs as shown
+## below, closes the loop, and then permutes inputs and outputs back to their
+## original order
+## @example
+## @group
+##                  ____________________
+##  u_1       ----->|                  |----> y_1
+##                  |        sys       |
+##          old u_2 |                  |
+## u_2* ---->(+)--->|                  |----->y_2
+## (in_idx)   ^     -------------------|    | (out_idx)
+##            |                             |
+##            -------------------------------
+## @end group
+## @end example
+## The input that has the summing junction added to it has an * added to
+## the end  of the input name.
+## @end deftypefn
+
+## Author: A. S. Hodel <a.s.hodel@eng.auburn.edu>
+## Created: August 1995
+## modified by John Ingram July 1996
+
+function sys = sysconnect (sys, output_list, input_list, order, tol)
+
+  if( (nargin < 3) | (nargin > 5) )
+    usage("retsys = sysconnect(sys,output_list,input_list[,order,tol])");
+  endif
+
+  ## check order
+  if(nargin <= 3)
+    order = 0;
+  elseif( (order != 0) & (order != 1) )
+    error("sysconnect: order must be either 0 or 1")
+  endif
+
+  if (nargin <= 4)
+    tol = 200*eps;
+  elseif( !is_sample(tol) )
+    error("sysconnect: tol must be a positive scalar");
+  elseif(tol > 1e2*sqrt(eps))
+    warning(["sysconnect: tol set to large value=",num2str(tol), ...
+        ", eps=",num2str(eps)])
+  endif
+
+  ## verify sizes,format of input, output lists
+  if( min(size(output_list))*min(size(input_list)) != 1)
+    error("output_list and input_list must be vectors");
+  else
+    lo = length(output_list);
+    li = length(input_list);
+    if(lo != li)
+      error("output_list and input_list must be of the same length")
+    endif
+
+    if(is_duplicate_entry(output_list) | is_duplicate_entry(input_list) )
+      error("duplicate entry in input_list and/or output_list");
+    endif
+  endif
+
+  [nc,nz,mm,pp] = sysdimensions(sys);
+  nn = nc+nz;
+
+  if( !is_struct(sys))
+    error("sys must be in structured system form")
+  elseif(pp < li)
+    error(["length(output_list)=",num2str(li),", sys has only ", ...
+        num2str(pp),"system outputs"])
+  elseif(mm < li)
+    error(["length(input_list)=",num2str(li),", sys has only ", ...
+        num2str(mm),"system inputs"])
+  endif
+
+  ## check that there are enough inputs/outputs in the system for the lists
+  if(max(input_list) > mm)
+    error("max(input_list) exceeds the number of inputs");
+  elseif(max(output_list) > pp)
+    error("max(output_list) exceeds the number of outputs");
+  endif
+
+  output_list = reshape(output_list,1,length(output_list));
+
+  ## make sure we're in state space form
+  sys = sysupdate (sys, "ss");
+
+  ## permute rows and columns of B,C,D matrices into pseudo-dgkf form...
+  all_inputs = sysreorder(mm,input_list);
+  all_outputs = sysreorder(pp,output_list);
+
+  [aa,bb,cc,dd] = sys2ss(sys);
+  bb = bb(:,all_inputs);
+  cc = cc(all_outputs,:);
+  dd = dd(all_outputs,all_inputs);
+
+  yd = sysgetsignals(sys,"yd");
+  yd = yd(all_outputs);
+
+  ## m1, p1 = number of inputs, outputs that are not being connected
+  m1 = mm-li;
+  p1 = pp-li;
+
+  ## m2, p2: 1st column, row of B, C that is being connected
+  m2 = m1+1;
+  p2 = p1+1;
+
+  ## partition system into a DGKF-like form; the loop is closed around
+  ## B2, C2
+  if(m1 > 0)
+    B1 = bb(:,1:m1);
+    D21= dd(p2:pp,1:m1);
+  endif
+  B2 = bb(:,m2:mm);
+  if(p1 > 0)
+    C1 = cc(1:p1,:);
+    D12= dd(1:p1,m2:mm);
+  endif
+  C2 = cc(p2:pp,:);
+  if(m1*p1 > 0)
+    D11= dd(1:p1,1:m1);
+  endif
+  D22= dd(p2:pp,m2:mm);
+
+  if(norm(D22))
+    warning("sysconnect: possible algebraic loop, D22 non-zero");
+    D22i = (eye(size(D22))-D22);
+    C2h = D22i\C2;
+    if(m1 > 0)
+      D21h = D22i\D21;
+    endif
+    D22h = D22i\D22;
+  else
+    C2h = C2;
+    if(m1 > 0)
+      D21h = D21;
+    endif
+    D22h = D22;
+
+  endif
+
+  ## check cont state -> disc output -> cont state
+  dyi = find(yd(p2:pp));
+
+  ## disp("sysconnect: dyi=")
+  ## dyi
+  ## nc
+  ## disp("/sysconnect");
+
+  if( (nc > 0) & find(dyi > 0) )
+    B2con = B2(1:nc,dyi);       # connection to cont states
+    C2hd = C2h(dyi,1:nc);       # cont states -> outputs
+  else
+    B2con = C2hd = [];
+  endif
+
+  if(max(size(B2con)) & max(size(C2hd)) )
+    if(norm(B2con*C2hd))
+      warning("sysconnect: cont-state -> disc output -> cont state derivative");
+      warning("    connection made; resulting system may not be meaningful");
+    endif
+  endif
+
+  Ac = aa+B2*C2h;
+  if(m1 > 0)
+    B1c = B1 + B2*D21h;
+  endif
+  B2c = B2*(eye(size(D22h)) + D22h);
+  if(p1*m1 > 0)
+    D11c = D11 + D12*D21h;
+  endif
+  if(p1 > 0)
+    C1c  = C1+D12*C2h;
+    D12c = D12*(eye(size(D22h))+D22h);
+  endif
+
+  ## construct system data structure
+  if(m1 > 0)
+   Bc = [B1c, B2c];
+  else
+   Bc = B2c;
+  endif
+
+  if(p1 > 0)
+    Cc = [C1c;C2h];
+  else
+    Cc = C2h;
+  endif
+
+  if(m1*p1 > 0)
+    Dc = [D11c,D12c; D21h,D22h];
+  elseif(m1 > 0)
+    Dc = [D21h, D22h];
+  elseif(p1 > 0)
+    Dc = [D12c; D22h];
+  else
+    Dc = D22h;
+  endif
+
+  ## permute rows and columns of Bc, Cc, Dc back into original order
+  Im = eye(mm,mm);
+  Pi = Im(:,all_inputs);
+  back_inputs = Pi*[1:mm]';
+
+  Ip = eye(pp,pp);
+  Po = Ip(:,all_outputs);
+  back_outputs = Po*[1:pp]';
+
+  Bc = Bc(:,back_inputs);
+  Cc = Cc(back_outputs,:);
+  Dc = Dc(back_outputs,back_inputs);
+  yd = yd(back_outputs);
+
+  ## rebuild system
+  Ts = sysgettsam(sys);
+  [stnam,innam,outnam] = sysgetsignals(sys);
+  sys = ss2sys(Ac,Bc,Cc,Dc,Ts,nc,nz,stnam,innam,outnam,find(yd));
+
+  ## update connected input names
+  for ii = 1:length(input_list)
+    idx = input_list(ii);
+    strval = sprintf("%s*",nth(sysgetsignals(sys,"in",idx),1) );
+    sys = syssetsignals(sys,"in",strval,idx);
+  endfor
+
+  ## maintain original system type if it was SISO
+  if (strcmp (sysgettype (sys), "tf"))
+    sysupdate (sys, "tf");
+  elseif (strcmp (sysgettype (sys),"zp"))
+    sysupdate (sys, "zp");
+  endif
+
+endfunction