/usr/share/octave/packages/signal-1.3.2/cceps.m is in octave-signal 1.3.2-1+b1.
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 program 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.
##
## This program 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
## this program; if not, see <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @deftypefn {Function File} {} cceps (@var{x})
## @deftypefnx {Function File} {} cceps (@var{x}, @var{correct})
## Return the complex cepstrum of the vector @var{x}.
## If the optional argument @var{correct} has the value 1, a correction
## method is applied. The default is not to do this.
## @end deftypefn
## Author: Andreas Weingessel <Andreas.Weingessel@ci.tuwien.ac.at>
## Apr 1, 1994
## Last modified by AW on Nov 8, 1994
function cep = cceps (x, c)
if (nargin == 1)
c = 0;
elseif (nargin != 2)
print_usage;
endif
[nr, nc] = size (x);
if (nc != 1)
if (nr == 1)
x = x';
nr = nc;
else
error ("cceps: x must be a vector");
endif
endif
bad_signal_message = ["cceps: bad signal x, ", ...
"some Fourier coefficients are zero."];
F = fft (x);
if (min (abs (F)) == 0)
error (bad_signal_message);
endif
## determine if correction necessary
half = fix (nr / 2);
cor = 0;
if (2 * half == nr)
cor = (c && (real (F (half + 1)) < 0));
if (cor)
F = fft (x(1:nr-1))
if (min (abs (F)) == 0)
error (bad_signal_message);
endif
endif
endif
cep = fftshift (ifft (log (F)));
## make result real
if (c)
cep = real (cep);
if (cor)
## make cepstrum of same length as input vector
cep (nr) = 0;
endif
endif
endfunction
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