--- a/scripts/control/sysgroup.m
+++ b/scripts/control/sysgroup.m
@@ -1,4 +1,4 @@
-# Copyright (C) 1996,1998 A. Scottedward Hodel 
+# Copyright (C) 1996, 1998, 1999 Auburn University.  All Rights Reserved.
 #
 # This file is part of Octave. 
 #
@@ -16,12 +16,15 @@
 # along with Octave; see the file COPYING.  If not, write to the Free 
 # Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. 
  
-function sys = sysgroup(Asys,Bsys)
-# function sys = sysgroup(Asys,Bsys)
-# Combines two system data structures into a single system
+function sys = sysgroup(...)
+# function sys = sysgroup(Asys{,Bsys,...})
+# Parallel connection of systems
 #
-# input: Asys, Bsys: system data structures
-# output: sys: Asys and Bsys are combined into a single system:
+# inputs: All input arguments must be system data structures;
+#         exits with an error if there is not at least one argument
+# output: sys: all systems are combined into a single system; e.g.,
+#         if two systems are passed as sysgroup(Asys,Bsys), the result
+#         is
 #
 #              __________________
 #              |    ________    |
@@ -36,10 +39,11 @@
 # The function also rearranges the A,B,C matrices so that the 
 # continuous states come first and the discrete states come last.
 # If there are duplicate names, the second name has a unique suffix appended
-# on to the end of the name.
+# on to the end of the name (a warning message is printed).
 
 # A. S. Hodel August 1995
 # modified by John Ingram July 1996
+# A. S. Hodel: modified for variable number of arguments 1999
 
   save_val = implicit_str_to_num_ok;	# save for later
   implicit_str_to_num_ok = 1;
@@ -47,75 +51,98 @@
   save_emp = empty_list_elements_ok;
   empty_list_elements_ok = 1;
 
-  if(nargin ~= 2)
-    usage("sys = sysgroup(Asys,Bsys)");
-  elseif( !is_struct(Asys) | !is_struct(Bsys) )
-    error("sysgroup: input arguments must both be structured systems");
-  endif
-
-  # extract information from Asys, Bsys to consruct sys
-  Asys = sysupdate(Asys,"ss");
-  Bsys = sysupdate(Bsys,"ss");
-  [n1,nz1,m1,p1] = sysdimensions(Asys);
-  [n2,nz2,m2,p2] = sysdimensions(Bsys);
-  [Aa,Ab,Ac,Ad,Atsam,An,Anz,Ast,Ain,Aout,Ayd] = sys2ss(Asys);
-  [Ba,Bb,Bc,Bd,Btsam,Bn,Bnz,Bst,Bin,Bout,Byd] = sys2ss(Bsys);
-  nA = An + Anz;
-  nB = Bn + Bnz;
-
-  if(p1*m1*p2*m2 == 0)
-    error("sysgroup: argument lacks inputs and/or outputs");
-
-  elseif((Atsam + Btsam > 0) & (Atsam * Btsam == 0) )
-    warning("sysgroup: creating combination of continuous and discrete systems")
-
-  elseif(Atsam != Btsam)
-    error("sysgroup: Asys.tsam=%e, Bsys.tsam =%e", Atsam, Btsam);
+    
+  if(nargin < 1)
+    usage("sys = sysgroup(Asys{,Bsys,...})");
   endif
 
-  A = [Aa,zeros(nA,nB); zeros(nB,nA),Ba];
-  B = [Ab,zeros(nA,m2); zeros(nB,m1),Bb];
-  C = [Ac,zeros(p1,nB); zeros(p2,nA),Bc];
-  D = [Ad,zeros(p1,m2); zeros(p2,m1),Bd];
-  tsam = max(Atsam,Btsam);
-
-  # construct combined signal names; stnames must check for pure gain blocks
-  if(isempty(Ast))
-    stname = Bst;
-  elseif(isempty(Bst))
-    stname = Ast;
-  else
-    stname  = append(Ast, Bst);
-  endif
-  inname  = append(Ain, Bin);
-  outname = append(Aout,Bout);
+  # collect all arguments
+  arglist = list();
+  va_start();
+  for kk=1:nargin
+    arglist(kk) = va_arg();
+    if(!is_struct(nth(arglist,kk)))
+      error("sysgroup: argument %d is not a data structure",kk);
+    endif
+  endfor
 
-  # Sort states into continous first, then discrete
-  dstates = ones(1,(nA+nB));
-  if(An)
-    dstates(1:(An)) = zeros(1,An);
-  endif
-  if(Bn)
-    dstates((nA+1):(nA+Bn)) = zeros(1,Bn);
+  if(nargin == 2)
+    # the usual case; group the two systems together
+    Asys = nth(arglist,1);
+    Bsys = nth(arglist,2);
+  
+    # extract information from Asys, Bsys to consruct sys
+    Asys = sysupdate(Asys,"ss");
+    Bsys = sysupdate(Bsys,"ss");
+    [n1,nz1,m1,p1] = sysdimensions(Asys);
+    [n2,nz2,m2,p2] = sysdimensions(Bsys);
+    [Aa,Ab,Ac,Ad,Atsam,An,Anz,Ast,Ain,Aout,Ayd] = sys2ss(Asys);
+    [Ba,Bb,Bc,Bd,Btsam,Bn,Bnz,Bst,Bin,Bout,Byd] = sys2ss(Bsys);
+    nA = An + Anz;
+    nB = Bn + Bnz;
+  
+    if(p1*m1*p2*m2 == 0)
+      error("sysgroup: argument lacks inputs and/or outputs");
+  
+    elseif((Atsam + Btsam > 0) & (Atsam * Btsam == 0) )
+      warning("sysgroup: creating combination of continuous and discrete systems")
+  
+    elseif(Atsam != Btsam)
+      error("sysgroup: Asys.tsam=%e, Bsys.tsam =%e", Atsam, Btsam);
+    endif
+  
+    A = [Aa,zeros(nA,nB); zeros(nB,nA),Ba];
+    B = [Ab,zeros(nA,m2); zeros(nB,m1),Bb];
+    C = [Ac,zeros(p1,nB); zeros(p2,nA),Bc];
+    D = [Ad,zeros(p1,m2); zeros(p2,m1),Bd];
+    tsam = max(Atsam,Btsam);
+  
+    # construct combined signal names; stnames must check for pure gain blocks
+    if(isempty(Ast))
+      stname = Bst;
+    elseif(isempty(Bst))
+      stname = Ast;
+    else
+      stname  = append(Ast, Bst);
+    endif
+    inname  = append(Ain, Bin);
+    outname = append(Aout,Bout);
+  
+    # Sort states into continous first, then discrete
+    dstates = ones(1,(nA+nB));
+    if(An)
+      dstates(1:(An)) = zeros(1,An);
+    endif
+    if(Bn)
+      dstates((nA+1):(nA+Bn)) = zeros(1,Bn);
+    endif
+    [tmp,pv] = sort(dstates);
+    A = A(pv,pv);
+    B = B(pv,:);
+    C = C(:,pv);
+    stname = stname(pv);
+  
+    # check for duplicate signal names
+    inname = sysgroupn(inname,"input");
+    stname = sysgroupn(stname,"state");
+    outname = sysgroupn(outname,"output");
+  
+    # mark discrete outputs
+    outlist = find([Ayd, Byd]);
+  
+    # build new system
+    sys = ss2sys(A,B,C,D,tsam,An+Bn,Anz+Bnz,stname,inname,outname);
+
+  else
+    # multiple systems (or a single system); combine together one by one
+    sys = nth(arglist,1);
+    for kk=2:length(arglist)
+      printf("sysgroup: kk=%d\n",kk);
+      sys = sysgroup(sys,nth(arglist,kk));
+    endfor
   endif
-  [tmp,pv] = sort(dstates);
-  A = A(pv,pv);
-  B = B(pv,:);
-  C = C(:,pv);
-  stname = stname(pv);
-
-  # check for duplicate signal names
-  inname = sysgroupn(inname,"input");
-  stname = sysgroupn(stname,"state");
-  outname = sysgroupn(outname,"output");
-
-  # mark discrete outputs
-  outlist = find([Ayd, Byd]);
-
-  # build new system
-  sys = ss2sys(A,B,C,D,tsam,An+Bn,Anz+Bnz,stname,inname,outname);
-
+  
   implicit_str_to_num_ok = save_val;	# restore value  
   empty_list_elements_ok = save_emp;
-
+    
 endfunction