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## Copyright (C) 1996, 1998, 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{a}, @var{b}, @var{c}, @var{d}, @var{tsam}, @var{n}, @var{nz}, @var{stname}, @var{inname}, @var{outname}, @var{yd}] =} sys2ss (@var{sys})
## Extract state space representation from system data structure.
##
## @strong{Input}
## @table @var
## @item sys
## System data structure.
## @end table
##
## @strong{Outputs}
## @table @var
## @item a
## @itemx b
## @itemx c
## @itemx d
## State space matrices for @var{sys}.
##
## @item tsam
## Sampling time of @var{sys} (0 if continuous).
##
## @item n
## @itemx nz
## Number of continuous, discrete states (discrete states come
## last in state vector @var{x}).
##
## @item stname
## @itemx inname
## @itemx outname
## Signal names (lists of strings); names of states,
## inputs, and outputs, respectively.
##
## @item yd
## Binary vector; @var{yd}(@var{ii}) is 1 if output @var{y}(@var{ii})
## is discrete (sampled); otherwise @var{yd}(@var{ii}) is 0.
##
## @end table
## A warning massage is printed if the system is a mixed
## continuous and discrete system.
##
## @strong{Example}
## @example
## octave:1> sys=tf2sys([1 2],[3 4 5]);
## octave:2> [a,b,c,d] = sys2ss(sys)
## a =
## 0.00000 1.00000
## -1.66667 -1.33333
## b =
## 0
## 1
## c = 0.66667 0.33333
## d = 0
## @end example
## @end deftypefn
## Author: David Clem
## Created: August 19, 1994
## Updates by John Ingram July 14, 1996
function [a, b, c, d, tsam, n, nz, stname, inname, outname, yd] = sys2ss (sys)
if (nargin != 1)
print_usage ();
endif
if (! isstruct (sys))
error ("input argument must be a system data structure");
endif
sys = sysupdate (sys, "ss"); # make sure state space data is there
[n, nz, m, p] = sysdimensions (sys);
[stname, inname, outname, yd] = sysgetsignals (sys);
tsam = sysgettsam (sys);
cont = sum (yd == 0) + n;
dig = sum (yd != 0) + nz + tsam;
if (cont*dig)
warning ("sys2ss: input system is mixed continuous/discrete");
endif
a = sys.a;
b = sys.b;
c = sys.c;
d = sys.d;
endfunction
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