Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / control-2.3.52 / dss.m

diff --git a/octave_packages/control-2.3.52/dss.m b/octave_packages/control-2.3.52/dss.m
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+## Copyright (C) 2010   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{sys} =} dss (@var{sys})
+## @deftypefnx {Function File} {@var{sys} =} dss (@var{d})
+## @deftypefnx {Function File} {@var{sys} =} dss (@var{a}, @var{b}, @var{c}, @var{d}, @var{e}, @dots{})
+## @deftypefnx {Function File} {@var{sys} =} dss (@var{a}, @var{b}, @var{c}, @var{d}, @var{e}, @var{tsam}, @dots{})
+## Create or convert to descriptor state-space model.
+##
+## @strong{Inputs}
+## @table @var
+## @item sys
+## LTI model to be converted to state-space.
+## @item a
+## State transition matrix (n-by-n).
+## @item b
+## Input matrix (n-by-m).
+## @item c
+## Measurement matrix (p-by-n).
+## @item d
+## Feedthrough matrix (p-by-m).
+## @item e
+## Descriptor matrix (n-by-n).
+## @item tsam
+## Sampling time in seconds.  If @var{tsam} is not specified, 
+## a continuous-time model is assumed.
+## @item @dots{}
+## Optional pairs of properties and values.
+## Type @command{set (dss)} for more information.
+## @end table
+##
+## @strong{Outputs}
+## @table @var
+## @item sys
+## Descriptor state-space model.
+## @end table
+##
+## @strong{Equations}
+## @example
+## @group
+##   .
+## E x = A x + B u
+##   y = C x + D u
+## @end group
+## @end example
+##
+## @seealso{ss, tf}
+## @end deftypefn
+
+## Author: Lukas Reichlin <lukas.reichlin@gmail.com>
+## Created: September 2010
+## Version: 0.1
+
+function sys = dss (varargin)
+
+  switch (nargin)
+    case {0, 1}  # static gain (dss (5)) or empty (useful for "set (dss)")
+      sys = ss (varargin{:});
+
+    case {2, 3, 4}
+      print_usage ();
+
+    otherwise    # general case
+      sys = ss (varargin{[1:4, 6:end]}, "e", varargin{5});
+  endswitch
+
+endfunction
+
+## NOTE: The author prefers "dss (e, a, b, c, d)" since we write
+##         .
+##       E x = A x + B u,     y = C x + D u
+##
+##       but this would break compatibility to a widespread
+##       commercial implementation of the octave language.
+##       There's no way to tell e and d apart if n = m = p.