--- /dev/null
+## Copyright (C) 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 -*-
+## @deftypefn{Function File} {@var{hsv} =} hsvd (@var{sys})
+## @deftypefnx{Function File} {@var{hsv} =} hsvd (@var{sys}, @var{"offset"}, @var{offset})
+## @deftypefnx{Function File} {@var{hsv} =} hsvd (@var{sys}, @var{"alpha"}, @var{alpha})
+## Hankel singular values of the stable part of an LTI model. If no output arguments are
+## given, the Hankel singular values are displayed in a plot.
+##
+## @strong{Algorithm}@*
+## Uses SLICOT AB13AD by courtesy of
+## @uref{http://www.slicot.org, NICONET e.V.}
+## @end deftypefn
+
+## Author: Lukas Reichlin <lukas.reichlin@gmail.com>
+## Created: January 2010
+## Version: 0.4
+
+function hsv_r = hsvd (sys, prop = "offset", val = 1e-8)
+
+ if (nargin != 1 && nargin != 3)
+ print_usage ();
+ endif
+
+ if (! isa (sys, "lti"))
+ error ("hsvd: first argument must be an LTI system");
+ endif
+
+ if (! is_real_scalar (val))
+ error ("hsvd: third argument must be a real scalar");
+ endif
+
+ [a, b, c, ~, ~, scaled] = ssdata (sys);
+
+ discrete = ! isct (sys);
+
+ switch (tolower (prop(1)))
+ case "o" # offset
+ if (discrete)
+ alpha = 1 - val;
+ else
+ alpha = - val;
+ endif
+ case "a" # alpha
+ alpha = val;
+ otherwise
+ error ("hsvd: second argument invalid");
+ endswitch
+
+ [hsv, ns] = slab13ad (a, b, c, discrete, alpha, scaled);
+
+ if (nargout)
+ hsv_r = hsv;
+ else
+ bar ((1:ns) + (rows (a) - ns), hsv);
+ title (["Hankel Singular Values of Stable Part of ", inputname(1)]);
+ xlabel ("State");
+ ylabel ("State Energy");
+ grid ("on");
+ endif
+
+endfunction
+
+
+%!shared hsv, hsv_exp
+%! a = [ -0.04165 0.0000 4.9200 -4.9200 0.0000 0.0000 0.0000
+%! -5.2100 -12.500 0.0000 0.0000 0.0000 0.0000 0.0000
+%! 0.0000 3.3300 -3.3300 0.0000 0.0000 0.0000 0.0000
+%! 0.5450 0.0000 0.0000 0.0000 -0.5450 0.0000 0.0000
+%! 0.0000 0.0000 0.0000 4.9200 -0.04165 0.0000 4.9200
+%! 0.0000 0.0000 0.0000 0.0000 -5.2100 -12.500 0.0000
+%! 0.0000 0.0000 0.0000 0.0000 0.0000 3.3300 -3.3300];
+%!
+%! b = [ 0.0000 0.0000
+%! 12.5000 0.0000
+%! 0.0000 0.0000
+%! 0.0000 0.0000
+%! 0.0000 0.0000
+%! 0.0000 12.500
+%! 0.0000 0.0000];
+%!
+%! c = [ 1.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
+%! 0.0000 0.0000 0.0000 1.0000 0.0000 0.0000 0.0000
+%! 0.0000 0.0000 0.0000 0.0000 1.0000 0.0000 0.0000];
+%!
+%! sys = ss (a, b, c, [], "scaled", true);
+%! hsv = hsvd (sys, "alpha", 0.0);
+%!
+%! hsv_exp = [2.5139; 2.0846; 1.9178; 0.7666; 0.5473; 0.0253; 0.0246];
+%!
+%!assert (hsv, hsv_exp, 1e-4);