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## Copyright (C) 1996, 1999, 2000, 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{digital} =} is_digital (@var{sys}, @var{eflg})
## Return nonzero if system is digital.
##
## @strong{Inputs}
## @table @var
## @item sys
## System data structure.
## @item eflg
## When equal to 0 (default value), exits with an error if the system
## is mixed (continuous and discrete components); when equal to 1, print
## a warning if the system is mixed (continuous and discrete); when equal
## to 2, operate silently.
## @end table
##
## @strong{Output}
## @table @var
## @item digital
## When equal to 0, the system is purely continuous; when equal to 1, the
## system is purely discrete; when equal to -1, the system is mixed continuous
## and discrete.
## @end table
## Exits with an error if @var{sys} is a mixed (continuous and discrete) system.
## @end deftypefn
## Author: A. S. Hodel <a.s.hodel@eng.auburn.edu>
## Created: July 1996
function DIGITAL = is_digital (sys, eflg)
switch (nargin)
case 1
eflg = 0;
case 2
if (isempty (find (eflg == [0, 1, 2])))
error ("invalid value of eflg=%g", eflg);
endif
otherwise,
print_usage ();
endswitch
## checked for sampled data system (mixed)
## discrete system
sysyd = sysgetsignals (sys, "yd");
[nn, nz] = sysdimensions (sys);
cont = sum (sysyd == 0) + nn;
tsam = sysgettsam (sys);
dig = sum (sysyd != 0) + nz + tsam;
## check for mixed system
if (cont*dig != 0)
switch (eflg)
case 0
error ("continuous/discrete system; use syscont, sysdisc, or c2d first");
case 1
warning ("is_digital: mixed continuous/discrete system");
endswitch
dig_sign = -1;
else
dig_sign = 1;
endif
DIGITAL = dig_sign*(tsam > 0);
endfunction
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