## Copyright (C) 2009-2016 Lukas F. Reichlin
##
## This file is part of LTI Syncope.
##
## LTI Syncope 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.
##
## LTI Syncope 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 LTI Syncope. If not, see <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @deftypefn {Function File} {@var{augsys} =} augstate (@var{sys})
## Append state vector x of system @var{sys} to output vector y.
##
## @example
## @group
## . .
## x = A x + B u x = A x + B u
## y = C x + D u => y = C x + D u
## x = I x + O u
## @end group
## @end example
##
## @end deftypefn
## Author: Lukas Reichlin <lukas.reichlin@gmail.com>
## Created: October 2015
## Version: 0.1
function augsys = augstate (sys)
if (nargin != 1 || ! isa (sys, "lti"))
print_usage ();
endif
if (! isa (sys, "ss"))
warning ("augstate: system not in state-space form");
sys = ss (sys);
endif
[a, b, c, d, e, tsam] = dssdata (sys, []);
[inn, stn, outn, ing, outg] = get (sys, "inname", "stname", "outname", "ingroup", "outgroup");
[p, m] = size (d);
n = rows (a);
caug = vertcat (c, eye (n));
daug = vertcat (d, zeros (n, m));
outname = vertcat (outn, stn);
augsys = dss (a, b, caug, daug, e, tsam);
augsys = set (augsys, "inname", inn, "stname", stn, "outname", outname, ...
"ingroup", ing, "outgroup", outg);
endfunction