--- a/scripts/control/is_signal_list.m
+++ b/scripts/control/is_signal_list.m
@@ -1,36 +1,32 @@
-## 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.
+# Copyright (C) 1996,1998,2000 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, 675 Mass Ave, Cambridge, MA 02139, USA.
 
-## -*- texinfo -*-
-## @deftypefn {Function File} {@var{flg} =} is_signal_list (@var{mylist})
-## Returns true if mylist is a list of individual strings (legal for
-## input to @var{syssetsignals}).
-## @end deftypefn
-
-function flg = is_signal_list (mylist)
-
-  flg = is_list(mylist);
-  if(flg)
-    for ii=1:length(mylist)
-      if(!(isstr(nth(mylist,ii)) & rows(nth(mylist,ii)) ==1) )
-	flg = 0;
-      endif
-    endfor
-  endif
+function flg = is_signal_list(mylist)
+# function flg = is_signal_list(mylist)
+# returns true if mylist is a list of individual strings.
+# 
+flg = is_list(mylist);
+if(flg)
+  for ii=1:length(mylist)
+    if(!(isstr(nth(mylist,ii)) & rows(nth(mylist,ii)) ==1) )
+      flg = 0;
+    endif
+  endfor
+endif
 
 endfunction

--- a/scripts/control/listidx.m
+++ b/scripts/control/listidx.m
@@ -1,4 +1,4 @@
-## Copyright (C) 1996, 1998 Auburn University.  All rights reserved.
+## Copyright (C) 2000 Auburn University.  All rights reserved.
 ##
 ## This file is part of Octave.
 ##
@@ -16,31 +16,24 @@
 ## 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{idxvec}, @var{errmsg}] =} listidx(@var{listvar}, @var{strlist})
+## [idxvec, errmsg] = listidx(listvar, strlist)
 ## return indices of string entries in listvar that match strings in strlist
-## @strong{Inputs}
-## @table @var
-## @item listvar
-##   list of strings to be searched
-## @item strlist
-##   list of strings to be located in listvar.
-## @end table
-## @strong{Note} @var{listvar}, @var{strlist} may be passed as strings or 
-##    string matrices; in this case, each entry is processed by deblank() 
-##    prior to searching for the entries of @var{strlist} in @var{listvar}.
-## @strong{Outputs}
-## @table @var
-## @item idxvec
-##    vector of indices in @var{listvar};
-##    @var{listvar}(@var{idxvec}(@var{k})) == @var{strlist}(@var{kk}).
-## @item errmsg
-##    if strlist contains a string not in @var{listvar}, then
-##    an error message is returned in @var{errmsg}.  If only one output
-##    argument is requested, e.g., @code{idxvec = listidex(listvar, strlist)},
-##    then @var{listidx} prints @var{errmsg} to the screen and exits with 
+## Inputs:
+##   listvar: list of strings to be searched
+##   strlist: list of strings to be located in listvar.
+## Note: listvar, strlist may be passed as strings or string matrices; 
+##    in this case, each entry is processed by deblank() prior to searching 
+##    for the entries of strlist in listvar.
+## Outputs:
+## idxvec
+##    vector of indices in listvar;
+##    listvar(idxvec(k)) == strlist(kk).
+## errmsg
+##    if strlist contains a string not in listvar, then
+##    an error message is returned in errmsg.  If only one output
+##    argument is requested, e.g., idxvec = listidx(listvar, strlist),
+##    then listidx prints errmsg to the screen and exits with 
 ##    an error.
-## @end table
 ##
 
 function [idxvec,errmsg]  = listidx(listvar,strlist)
@@ -55,7 +48,6 @@
   for kk=1:rows(tmp)
     strlist(kk) = deblank(tmp(kk,:));
   endfor
-  strlist
 endif
 
 if(isstr(listvar))
@@ -66,12 +58,23 @@
   endfor
 endif
 
-if(!is_signal_list(listvar))     error("listvar must be a list of strings");
-elseif(!is_signal_list(strlist)) error("strlist must be a list of strings");
+## initialize size of idxvec (for premature return)
+idxvec = zeros(length(strlist),1);
+
+errmsg = "";
+if(!is_signal_list(listvar))
+  errmsg = "listvar must be a list of strings";
+elseif(!is_signal_list(strlist))
+  errmsg = "strlist must be a list of strings";
+endif
+
+if(length(errmsg))
+  if(nargout < 2) error(errmsg); 
+  else return;
+  endif
 endif
 
 nsigs = length(listvar);
-idxvec = zeros(length(strlist),1);
 for idx = 1:length(strlist)
   signame = nth(strlist,idx);
   for jdx = 1:nsigs

--- a/scripts/control/sysidx.m
+++ b/scripts/control/sysidx.m
@@ -1,74 +1,34 @@
-## Copyright (C) 1999 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.
-
-## idxvec = sysidx(sys,sigtype,signamelist)
-## return indices of signals with specified signal names
-## inputs:
-##   sys:         OCST system data structure
-##   sigtype:     signal type to be selected: "in", "out", "st"
-##   signamelist: list of desired signal names
-## outputs:
-##   idxvec: vector of signal indices (appropriate for use with sysprune)
-
-## Author: A. S. Hodel <a.s.hodel@eng.auburn.edu>
-
-function idxvec = sysidx (sys, sigtype, signamelist)
+function idxvec = sysidx(sys,sigtype,signamelist)
+# idxvec = sysidx(sys,sigtype,signamelist)
+# return indices of signals with specified signal names
+# inputs:
+#   sys:         OCST system data structure
+#   sigtype:     signal type to be selected: "in", "out", "st"
+#   signamelist: list of desired signal names
+# outputs:
+#   idxvec: vector of signal indices (appropriate for use with sysprune)
 
-  if(nargin != 3)         usage("idxvec = sysidx(sys,sigtype,signamelist)");
-  elseif(!is_struct(sys)) error("sys must be a system data structure");
-  elseif(!isstr(sigtype)) error("sigtype must be a string");
-  elseif(rows(sigtype) != 1) 
-			  error("sigtype (%d x %d) must be a single string", ...
-			    rows(sigtype),columns(sigtype));
-  elseif(!is_signal_list(signamelist)) 
-			  error("signamelist must be a list of strings");
-  endif
-
-  sigtype_list = list("input","output","state");
-  sigtnum = 0;
-  for idx = 1:length(sigtype_list)
-    thistype = nth(sigtype_list,idx);
-    if(strcmp(sigtype, thistype(1:length(sigtype)) )) sigtnum = idx; endif
-  endfor
-  if(sigtnum == 0)  error("Illegal sigtype value = %s\n",sigtype); endif
-
-  syssiglist = sysgetsignals(sys,sigtype);
+if(nargin != 3)
+  usage("idxvec = sysidx(sys,sigtype,signamelist)");
+elseif(!is_struct(sys))
+  error("sys must be a system data structure");
+elseif(!isstr(sigtype))
+  error("sigtype must be a string");
+elseif(rows(sigtype) != 1) 
+  error("sigtype (%d x %d) must be a single string", ...
+    rows(sigtype),columns(sigtype));
+end
 
-  for idx = 1:length(signamelist)
-    signame = nth(signamelist,idx);
-    idxvec(idx) = 0;
-    nsigs = sysdimensions(sys,sigtype);
-    for jdx = 1:nsigs
-      ## printf("idx=%d jdx=%d signame=-%s- thissig=-%s-\n",idx,jdx,signame, ...
-      ##   sysgetsignals(sys,sigtype,jdx,1));
-      if(strcmp(signame,sysgetsignals(sys,sigtype,jdx,1)))
-	if(idxvec(idx) != 0)
-	  warning("Duplicate system input %s (%d,%d)\n", ...
-	    sysgetsignals(sys,sigtype,jdx,1),jdx,idxvec(idx));
-	else
-	  idxvec(idx) = jdx;
-	endif
-      endif
-    endfor
-    if(idxvec(idx) == 0)
-      error("Did not find %s %s",nth(sigtype_list,sigtnum),signame);
-    endif
-  endfor
+# extract correct set of signal names values
+[idxvec,msg] = listidx( list("in","out","st","yd"), sigtype);
+if(msg)
+  error("Illegal sigtype=%s",sigtype);
+endif
 
+syssiglist = sysgetsignals(sys,sigtype);
+[idxvec,msg] = listidx(syssiglist,signamelist);
+if(length(msg))
+  error("sysidx(sigtype=%s): %s",sigtype, strrep(msg,"strlist","signamelist"));
+end
 
 endfunction