# Copyright (C) 1996 A. Scottedward Hodel 
#
# 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 2, 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, write to the Free 
# Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. 
 
function  SISO = is_siso(sys)
# function SISO = is_siso(sys)
# return nonzero if the system sys is single-input, single-output.

# a s hodel July 1996, 1998

  if(nargin != 1)
    usage("SISO = is_siso(sys)");
  elseif( !is_struct(sys))
    error("input must be a system structure (see ss2sys, tf2sys, zp2sys)");
  endif

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

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

endfunction