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## Copyright (C) 1996, 1999, 2000, 2002, 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{sys} =} syssub (@var{Gsys}, @var{Hsys})
## Return @math{sys = Gsys - Hsys}.
##
## @strong{Method}
##
## @var{Gsys} and @var{Hsys} are connected in parallel.
## The input vector is connected to both systems; the outputs are
## subtracted. Returned system names are those of @var{Gsys}.
## @example
## @group
## +--------+
## +--->| Gsys |---+
## | +--------+ |
## | +|
## u --+ (_)--> y
## | -|
## | +--------+ |
## +--->| Hsys |---+
## +--------+
## @end group
## @end example
## @end deftypefn
## Author: John Ingram <ingraje@eng.auburn.edu>
## Created: July 1996
## updated for variable numbers of input arguments by July 1999 A. S. Hodel
function sys = syssub (varargin)
if (nargin < 1)
print_usage ();
endif
## collect all arguments
arglist = {};
for kk = 1:nargin
arglist{kk} = varargin{kk};
if (! isstruct (arglist{kk}))
error ("syssub: argument %d is not a data structure", kk);
endif
endfor
## check system dimensions
[n, nz, mg, pg, Gyd] = sysdimensions (arglist{1});
for kk = 2:nargin
[n, nz, mh, ph, Hyd] = sysdimensions (arglist{kk});
if (mg != mh)
error ("arg 1 has %d inputs; arg %d has vs %d inputs", mg, kk, mh);
elseif (pg != ph)
error ("arg 1 has %d outputs; arg %d has vs %d outputs", pg, kk, ph);
elseif (norm (Gyd - Hyd))
warning ("cannot add a discrete output to a continuous output");
error ("Output type mismatch: arguments 1 and %d", kk);
endif
endfor
## perform the subtract
if (nargin == 2)
Gsys = arglist{1};
Hsys = arglist{2};
if (strcmp (sysgettype (Gsys), "tf") || strcmp (sysgettype (Hsys), "tf"))
## see if subtracting transfer functions with identical denominators
[Gnum, Gden, GT, Gin, Gout] = sys2tf (Gsys);
[Hnum, Hden, HT, Hin, Hout] = sys2tf (Hsys);
if (length (Hden) == length (Gden))
if ((Hden == Gden) & (HT == GT))
sys = tf (Gnum-Hnum, Gden, GT, Gin, Gout);
return;
endif
## if not, we go on and do the usual thing...
endif
endif
## make sure in ss form
Gsys = sysupdate (Gsys, "ss");
Hsys = sysupdate (Hsys, "ss");
## change signal names to avoid warning messages from sysgroup
Gsys = syssetsignals (Gsys, "in",
__sysdefioname__(length(Gin), "Gin_u"));
Gsys = syssetsignals (Gsys, "out",
__sysdefioname__(length(Gout), "Gout_u"));
Hsys = syssetsignals (Hsys, "in",
__sysdefioname__(length(Hin), "Hin_u"));
Hsys = syssetsignals (Hsys, "out",
__sysdefioname__(length(Hout), "Hout_u"));
sys = sysgroup (Gsys, Hsys);
eyin = eye (mg);
eyout = eye (pg);
sys = sysscale (sys, [eyout, -eyout], [eyin; eyin], Gout, Gin);
else
## multiple systems (or a single system); combine together one by one
sys = arglist{1};
for kk = 2:length(arglist)
sys = syssub (sys, arglist{kk});
endfor
endif
endfunction
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