--- /dev/null
+## Copyright (C) 2009, 2010 Lukas F. Reichlin
+## Copyright (C) 2009 Luca Favatella <slackydeb@gmail.com>
+##
+## 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{ob} =} obsv (@var{sys})
+## @deftypefnx {Function File} {@var{ob} =} obsv (@var{a}, @var{c})
+## Return observability matrix.
+##
+## @strong{Inputs}
+## @table @var
+## @item sys
+## LTI model.
+## @item a
+## State transition matrix (n-by-n).
+## @item c
+## Measurement matrix (p-by-n).
+## @end table
+##
+## @strong{Outputs}
+## @table @var
+## @item ob
+## Observability matrix.
+## @end table
+##
+## @strong{Equation}
+## @iftex
+## @tex
+## $$ O_b = \\left[ \\matrix{ C \\cr
+## CA \\cr
+## CA^2 \\cr
+## \\vdots \\cr
+## CA^{n-1} } \\right ] $$
+## @end tex
+## @end iftex
+## @ifnottex
+## @example
+## @group
+## | C |
+## | CA |
+## Ob = | CA^2 |
+## | ... |
+## | CA^(n-1) |
+## @end group
+## @end example
+## @end ifnottex
+## @end deftypefn
+
+## Author: Lukas Reichlin <lukas.reichlin@gmail.com>
+## Created: October 2009
+## Version: 0.2
+
+function ob = obsv (a, c)
+
+ if (nargin == 1) # obsv (sys)
+ ob = ctrb (a.').'; # transpose is overloaded for lti models
+ elseif (nargin == 2) # obsv (a, c)
+ ob = ctrb (a.', c.').'; # size checked inside
+ else
+ print_usage ();
+ endif
+
+endfunction
+
+
+%!assert (obsv ([1, 0; 0, -0.5], [8, 8]), [8, 8; 8, -4]);