/usr/share/octave/packages/signal-1.3.0/tukeywin.m is in octave-signal 1.3.0-1.
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} {@var{w} =} tukeywin (@var{L})
## @deftypefnx {Function File} {@var{w} =} tukeywin (@var{L}, @var{r})
## Return the filter coefficients of a Tukey window (also known as the
## cosine-tapered window) of length @var{L}. @var{r} defines the ratio
## between the constant section and and the cosine section. It has to be
## between 0 and 1. The function returns a Hanning window for @var{r}
## equal to 0 and a full box for @var{r} equals to 1. The default value of
## @var{r} is 1/2.
##
## For a definition of the Tukey window, see e.g. Fredric J. Harris,
## "On the Use of Windows for Harmonic Analysis with the Discrete Fourier
## Transform, Proceedings of the IEEE", Vol. 66, No. 1, January 1978,
## Page 67, Equation 38.
## @end deftypefn
function w = tukeywin (L, r = 1/2)
if (nargin < 1 || nargin > 2)
print_usage;
elseif (nargin == 2)
## check that 0 < r < 1
if r > 1
r = 1;
elseif r < 0
r = 0;
endif
endif
## generate window
switch r
case 0,
## full box
w = ones (L, 1);
case 1,
## Hanning window
w = hanning (L);
otherwise
## cosine-tapered window
t = linspace(0,1,L)(1:end/2)';
w = (1 + cos(pi*(2*t/r-1)))/2;
w(floor(r*(L-1)/2)+2:end) = 1;
w = [w; ones(mod(L,2)); flipud(w)];
endswitch
endfunction
%!demo
%! L = 100;
%! r = 1/3;
%! w = tukeywin (L, r);
%! title(sprintf("%d-point Tukey window, R = %d/%d", L, [p, q] = rat(r), q));
%! plot(w);
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