Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / control-2.3.52 / @ss / __d2c__.m

diff --git a/octave_packages/control-2.3.52/@ss/__d2c__.m b/octave_packages/control-2.3.52/@ss/__d2c__.m
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+++ b/octave_packages/control-2.3.52/@ss/__d2c__.m
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+## Copyright (C) 2011   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 -*-
+## Convert the discrete SS model into its continuous-time equivalent.
+
+## Author: Lukas Reichlin <lukas.reichlin@gmail.com>
+## Created: September 2011
+## Version: 0.2
+
+function sys = __d2c__ (sys, tsam, method = "zoh", w0 = 0)
+
+  switch (method(1))
+    case {"z", "s"}                # {"zoh", "std"}
+      [sys.a, sys.b, sys.c, sys.d, sys.e] = __dss2ss__ (sys.a, sys.b, sys.c, sys.d, sys.e);
+      [n, m] = size (sys.b);       # n: states, m: inputs
+      tmp = logm ([sys.a, sys.b; zeros(m,n), eye(m)]) / tsam;
+      if (norm (imag (tmp), inf) > sqrt (eps))
+        warning ("ss: d2c: possibly inaccurate results");
+      endif
+      sys.a = real (tmp(1:n, 1:n));
+      sys.b = real (tmp(1:n, n+1:n+m));
+
+    case {"t", "b", "p"}           # {"tustin", "bilin", "prewarp"}
+      if (method(1) == "p")        # prewarping
+        beta = w0 / tan (w0*tsam/2);
+      else
+        beta = 2/tsam;
+      endif
+      if (isempty (sys.e))
+        [sys.a, sys.b, sys.c, sys.d] = slab04md (sys.a, sys.b, sys.c, sys.d, 1, beta, true);
+      else
+        [sys.a, sys.b, sys.c, sys.d, sys.e] = __dss_bilin__ (sys.a, sys.b, sys.c, sys.d, sys.e, beta, true);
+      endif
+
+    otherwise
+      error ("ss: d2c: %s is an invalid or missing method", method);
+  endswitch
+
+endfunction