Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / control-2.3.52 / @ss / __sys_inverse__.m

diff --git a/octave_packages/control-2.3.52/@ss/__sys_inverse__.m b/octave_packages/control-2.3.52/@ss/__sys_inverse__.m
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+## Copyright (C) 2009, 2010, 2012   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 -*-
+## Inversion of SS models.
+
+## Author: Lukas Reichlin <lukas.reichlin@gmail.com>
+## Created: October 2009
+## Version: 0.3
+
+function sys = __sys_inverse__ (sys)
+
+  a = sys.a;
+  b = sys.b;
+  c = sys.c;
+  d = sys.d;
+  e = sys.e;
+
+  if (! isempty (e) || rcond (d) < eps)  # dss or strictly proper ss
+
+    n = rows (a);
+    m = columns (b);                     # p = m (square system)
+
+    if (isempty (e))                     # avoid testing twice?
+      e = eye (n);
+    endif
+
+    sys.a = [a, b; c, d];
+    sys.b = [zeros(n, m); -eye(m)];
+    sys.c = [zeros(m, n), eye(m)];
+    sys.d = zeros (m);
+    sys.e = [e, zeros(n, m); zeros(m, n+m)];
+
+    sys.stname = repmat ({""}, n+m, 1);
+
+  else                                   # proper ss
+
+    bid = b / d;
+
+    sys.a = a - bid * c;
+    sys.b = -bid;
+    sys.c = d \ c;
+    sys.d = inv (d);
+
+  endif
+
+endfunction
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