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## Copyright (C) 1993, 1994, 1995, 2000, 2002, 2003, 2004, 2005, 2006,
## 2007 Auburn University. All rights reserved.
##
##
## This program 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.
##
## This program 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 this program; see the file COPYING. If not, see
## <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @deftypefn {Function File} {@var{retval} =} is_detectable (@var{a}, @var{c}, @var{tol}, @var{dflg})
## @deftypefnx {Function File} {@var{retval} =} is_detectable (@var{sys}, @var{tol})
## Test for detectability (observability of unstable modes) of (@var{a}, @var{c}).
##
## Returns 1 if the system @var{a} or the pair (@var{a}, @var{c}) is
## detectable, 0 if not, and -1 if the system has unobservable modes at the
## imaginary axis (unit circle for discrete-time systems).
##
## @strong{See} @command{is_stabilizable} for detailed description of
## arguments and computational method.
## @seealso{is_stabilizable, size, rows, columns, length, ismatrix, isscalar, isvector}
## @end deftypefn
## Author: A. S. Hodel <a.s.hodel@eng.auburn.edu>
## Created: August 1993
## Updated by John Ingram (ingraje@eng.auburn.edu) July 1996.
function [retval, U] = is_detectable (a, c, tol, dflg)
if (nargin < 1)
print_usage ();
elseif (isstruct (a))
## system form
if (nargin == 2)
tol = c;
elseif (nargin > 2)
print_usage ();
endif
dflg = is_digital (a);
[a,b,c] = sys2ss (a);
else
if (nargin > 4 || nargin == 1)
print_usage ();
endif
if (! exist ("dflg"))
dflg = 0;
endif
endif
if (! exist ("tol"))
if (isa (a, "single") || isa (c, "single"))
tol = 200 * eps("single");
else
tol = 200 * eps;
endif
endif
retval = is_stabilizable (a', c', tol, dflg);
endfunction
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