/usr/share/octave/packages/signal-1.3.2/nuttallwin.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} {} nuttallwin (@var{m})
## @deftypefnx {Function File} {} nuttallwin (@var{m}, "periodic")
## @deftypefnx {Function File} {} nuttallwin (@var{m}, "symmetric")
## Return the filter coefficients of a Blackman-Harris window defined by
## Nuttall of length @var{m}.
##
## If the optional argument @code{"periodic"} is given, the periodic form
## of the window is returned. This is equivalent to the window of length
## @var{m}+1 with the last coefficient removed. The optional argument
## @code{"symmetric"} is equivalent to not specifying a second argument.
##
## @seealso{blackman, blackmanharris}
## @end deftypefn
function w = nuttallwin (m, opt)
if (nargin < 1 || nargin > 2)
print_usage ();
elseif (! (isscalar (m) && (m == fix (m)) && (m > 0)))
error ("nuttallwin: M must be a positive integer");
endif
N = m - 1;
if (nargin == 2)
switch (opt)
case "periodic"
N = m;
case "symmetric"
N = m - 1;
otherwise
error ("nuttallwin: window type must be either \"periodic\" or \"symmetric\"");
endswitch
endif
if (m == 1)
w = 1;
else
a0 = 0.355768;
a1 = 0.487396;
a2 = 0.144232;
a3 = 0.012604;
n = [-N/2:(m-1)/2]';
w = a0 + a1.*cos(2.*pi.*n./N) + a2.*cos(4.*pi.*n./N) + a3.*cos(6.*pi.*n./N);
endif
endfunction
%!assert (nuttallwin (1), 1)
%!assert (nuttallwin (2), zeros (2, 1), eps)
%!assert (nuttallwin (15), flipud (nuttallwin (15)), 10*eps);
%!assert (nuttallwin (16), flipud (nuttallwin (16)), 10*eps);
%!assert (nuttallwin (15), nuttallwin (15, "symmetric"));
%!assert (nuttallwin (16)(1:15), nuttallwin (15, "periodic"));
%% Test input validation
%!error nuttallwin ()
%!error nuttallwin (0.5)
%!error nuttallwin (-1)
%!error nuttallwin (ones (1, 4))
%!error nuttallwin (1, 2)
%!error nuttallwin (1, "invalid")
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