## Copyright (C) 1996, 2000, 2002, 2003, 2004, 2005, 2006, 2007
##               Auburn University.  All rights reserved.
##
## 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 3 of the License, 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, see
## <http://www.gnu.org/licenses/>.

## -*- texinfo -*-
## @deftypefn {Function File} {} is_siso (@var{sys})
## Returns nonzero if the system data structure
## @var{sys} is single-input, single-output.
## @end deftypefn

## Author: A. S. Hodel <a.s.hodel@eng.auburn.edu>
## Created: July 1996, 1998

function  SISO = is_siso (sys)

  if (nargin != 1)
    print_usage ();
  elseif (! isstruct (sys))
    error ("input must be a system structure (see ss, tf, zp)");
  endif

  [n, nz, m, p] = sysdimensions (sys);

  SISO = (m == 1 && p == 1);

endfunction