/usr/share/octave/packages/control-2.6.2/@tf/__minreal__.m is in octave-control 2.6.2-1build1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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##
## 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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