/usr/share/octave/packages/signal-1.3.2/flattopwin.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.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 | ## Author: Paul Kienzle <pkienzle@users.sf.net> (2004)
## This program is granted to the public domain.
## -*- texinfo -*-
## @deftypefn {Function File} {} flattopwin (@var{m})
## @deftypefnx {Function File} {} flattopwin (@var{m}, "periodic")
## @deftypefnx {Function File} {} flattopwin (@var{m}, "symmetric")
##
## Return the filter coefficients of a Flat Top window of length @var{m}.
## The Flat Top window is defined by the function f(w):
##
## @example
## @group
## f(w) = 1 - 1.93 cos(2 pi w) + 1.29 cos(4 pi w)
## - 0.388 cos(6 pi w) + 0.0322cos(8 pi w)
## @end group
## @end example
##
## where w = i/(m-1) for i=0:m-1 for a symmetric window, or
## w = i/m for i=0:m-1 for a periodic window. The default
## is symmetric. The returned window is normalized to a peak
## of 1 at w = 0.5.
##
## This window has low pass-band ripple, but high bandwidth.
##
## According to [1]:
##
## The main use for the Flat Top window is for calibration, due
## to its negligible amplitude errors.
##
## [1] Gade, S; Herlufsen, H; (1987) "Use of weighting functions in DFT/FFT
## analysis (Part I)", Bruel & Kjaer Technical Review No.3.
## @end deftypefn
function w = flattopwin (m, opt)
if (nargin < 1 || nargin > 2)
print_usage ();
elseif (! (isscalar (m) && (m == fix (m)) && (m > 0)))
error ("flattopwin: 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 ("flattopwin: window type must be either \"periodic\" or \"symmetric\"");
endswitch
endif
if (m == 1)
w = 1;
else
x = 2*pi*[0:m-1]'/N;
w = (1-1.93*cos(x)+1.29*cos(2*x)-0.388*cos(3*x)+0.0322*cos(4*x))/4.6402;
endif
endfunction
%!assert (flattopwin (1), 1);
%!assert (flattopwin (2), 0.0042 / 4.6402 * ones (2, 1), eps);
%!assert (flattopwin (15), flipud (flattopwin (15)), 10*eps);
%!assert (flattopwin (16), flipud (flattopwin (16)), 10*eps);
%!assert (flattopwin (15), flattopwin (15, "symmetric"));
%!assert (flattopwin (16)(1:15), flattopwin (15, "periodic"));
%% Test input validation
%!error flattopwin ()
%!error flattopwin (0.5)
%!error flattopwin (-1)
%!error flattopwin (ones (1, 4))
%!error flattopwin (1, 2)
%!error flattopwin (1, 2, 3)
%!error flattopwin (1, "invalid")
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