Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / control-2.3.52 / @tf / __minreal__.m

diff --git a/octave_packages/control-2.3.52/@tf/__minreal__.m b/octave_packages/control-2.3.52/@tf/__minreal__.m
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+## Copyright (C) 2009   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 -*-
+## Minimal realization of TF models.
+
+## Author: Lukas Reichlin <lukas.reichlin@gmail.com>
+## Created: October 2009
+## Version: 0.1
+
+function sys = __minreal__ (sys, tol)
+
+  ## TODO: Once ZPK models are implemented, convert TF to ZPK,
+  ##       do cancellations over there and convert back to TF
+
+  sqrt_eps = sqrt (eps);                        # treshold for zero
+
+  [p, m] = size (sys);
+
+  for ny = 1 : p
+    for nu = 1 : m
+      sisosys = __sys_prune__ (sys, ny, nu);
+
+      [zer, gain] = zero (sisosys);
+      pol = pole (sisosys);
+
+      for k = length (zer) : -1 : 1             # reversed because of deleted zeros
+        [~, idx] = min (abs (zer(k) - pol));    # find best match
+
+        if (tol == "def")
+          if (abs (zer(k)) < sqrt_eps)          # catch case zer(k) = 0
+            t = 1000 * eps;
+          else
+            t = 1000 * abs (zer(k)) * sqrt_eps;
+          endif
+        else
+          t = tol;
+        endif
+
+        if (abs (zer(k) - pol(idx)) < t)
+          zer(k) = [];
+          pol(idx) = [];
+        endif
+      endfor
+
+      num = real (gain * poly (zer));
+      den = real (poly (pol));
+
+      num_idx = find (abs (num) < sqrt_eps);    # suppress numerical noise
+      den_idx = find (abs (den) < sqrt_eps);    # in polynomial coefficients
+
+      num(num_idx) = 0;
+      den(den_idx) = 0;
+
+      sys.num{ny, nu} = tfpoly (num);
+      sys.den{ny, nu} = tfpoly (den);
+    endfor
+  endfor
+
+endfunction
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