new file mode 100644
--- /dev/null
+++ b/scripts/control/freqresp.m
@@ -0,0 +1,118 @@
+# Copyright (C) 1996,1998 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 [ff,w] = freqresp(sys,USEW,w);
+  # function [ff,w] = freqresp(sys,USEW{,w});
+  # Frequency response function - used internally by bode, nyquist.
+  # minimal argument checking; "do not attempt to do this at home"
+  # USEW returned by freqchkw 
+  # w: optional, must be present if USEW is given
+  #
+  # returns: ff = vector of finite G(j*w) entries (or || G(j*w) || for MIMO)
+  #          w = vector of frequencies used
+  #      ff and w are both returned as row vectors
+
+  #  Written by: R. Bruce Tenison July 11, 1994
+  # $Revision: 1.6 $
+  # SYS_INTERNAL accesses members of system data structure
+
+  save_val = empty_list_elements_ok;
+  empty_list_elements_ok = 1;
+
+  # Check Args
+  if( (nargin < 2) || (nargin > 4) )
+    usage ("[ff,w] = freqresp(sys,USEW{,w})");
+  elseif( USEW & (nargin < 3) )
+    error("USEW=1 but w was not passed.");
+  elseif( USEW & isempty(w))
+    warning("USEW=1 but w is empty; setting USEW=0");
+    USEW=0;
+  endif
+
+  DIGITAL = is_digital(sys);
+
+  # compute default w if needed
+  if(!USEW)
+    if(is_siso(sys))
+      sys = sysupdate(sys,"zp");
+      [zer,pol] = sys2zp(sys);
+    else
+      zer = tzero(sys);
+      pol = eig(sys2ss(sys));
+    endif
+
+    # get default frequency range
+    [wmin,wmax] = bode_bounds(zer,pol,DIGITAL,sysgettsam(sys));
+    w = logspace(wmin,wmax,50);
+  else
+    w = reshape(w,1,length(w)); 	# make sure it's a row vector
+  endif
+
+  # now get complex values of s or z
+  if(DIGITAL)
+    jw = exp(i*w*sysgettsam(sys));
+  else
+    jw = i*w;
+  endif
+
+  [nn,nz,mm,pp] = sysdimensions(sys);
+
+  # now compute the frequency response - divide by zero yields a warning
+  if (strcmp(sysgettype(sys),"zp"))
+    # zero-pole form (preferred)
+    [zer,pol,sysk] = sys2zp(sys);
+    ff = ones(size(jw));
+    l1 = min(length(zer)*(1-isempty(zer)),length(pol)*(1-isempty(pol)));
+    for ii=1:l1
+      ff = ff .* (jw - zer(ii)) ./ (jw - pol(ii));
+    endfor
+
+    # require proper  transfer function, so now just get poles.
+    for ii=(l1+1):length(pol)
+      ff = ff ./ (jw - pol(ii));
+    endfor
+    ff = ff*sysk;
+
+  elseif (strcmp(sysgettype(sys),"tf"))
+    # transfer function form 
+    [num,den] = sys2tf(sys);
+    ff = polyval(num,jw)./polyval(den,jw);
+  elseif (mm==pp)
+    # The system is square; do state-space form bode plot
+    [sysa,sysb,sysc,sysd,tsam,sysn,sysnz] = sys2ss(sys);
+    n = sysn + sysnz;
+    for ii=1:length(jw);
+      ff(ii) = det(sysc*((jw(ii).*eye(n)-sysa)\sysb)+sysd);
+    endfor;
+  else
+    # Must be state space... bode                            
+    [sysa,sysb,sysc,sysd,tsam,sysn,sysnz] = sys2ss(sys);
+    n = sysn + sysnz;
+    for ii=1:length(jw);
+      ff(ii) = norm(sysc*((jw(ii)*eye(n)-sysa)\sysb)+sysd);
+    endfor
+    
+  endif
+
+  w = reshape(w,1,length(w));
+  ff = reshape(ff,1,length(ff));
+
+  # restore global variable
+  empty_list_elements_ok = save_val;
+endfunction
+