--- /dev/null
+## Copyright (C) 2009, 2010, 2011 Lukas F. Reichlin
+##
+## This file is part of LTI Syncope.
+##
+## LTI Syncope 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 3 of the License, or
+## (at your option) any later version.
+##
+## LTI Syncope 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 LTI Syncope. If not, see <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## Frequency response of TF models.
+
+## Author: Lukas Reichlin <lukas.reichlin@gmail.com>
+## Created: October 2009
+## Version: 0.4
+
+function H = __freqresp__ (sys, w, resptype = 0, cellflag = false)
+
+ [num, den, tsam] = tfdata (sys, "vector");
+
+ if (isct (sys)) # continuous system
+ s = i * w;
+ else # discrete system
+ s = exp (i * w * abs (tsam));
+ endif
+
+ s = reshape (s, 1, 1, []);
+
+ if (issiso (sys))
+ H = polyval (num, s) ./ polyval (den, s);
+ else
+ H = cellfun (@(x, y) polyval (x, s) ./ polyval (y, s), num, den, "uniformoutput", false);
+ H = cell2mat (H);
+ endif
+
+ if (resptype)
+ [p, m] = size (sys);
+ l = length (s);
+ if (m != p)
+ error ("tf: freqresp: system must be square for response type %d", resptype);
+ endif
+ H = mat2cell (H, p, m, ones (1, l))(:);
+ j = eye (p);
+ switch (resptype)
+ case 1 # inversed system
+ H = cellfun (@inv, H, "uniformoutput", false);
+ case 2 # inversed sensitivity
+ H = cellfun (@(x) j + x, H, "uniformoutput", false);
+ case 3 # inversed complementary sensitivity
+ H = cellfun (@(x) j + inv (x), H, "uniformoutput", false);
+ otherwise
+ error ("tf: freqresp: invalid response type");
+ endswitch
+ if (! cellflag)
+ H = cat (3, H{:});
+ endif
+ elseif (cellflag)
+ [p, m] = size (sys);
+ l = length (s);
+ H = mat2cell (H, p, m, ones (1, l))(:);
+ endif
+
+endfunction