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## Copyright (C) 1995-2015 Friedrich Leisch
##
## This file is part of Octave.
##
## Octave 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.
##
## Octave 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 Octave; see the file COPYING. If not, see
## <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @deftypefn {Function File} {} spencer (@var{x})
## Return Spencer's 15 point moving average of each column of @var{x}.
## @end deftypefn
## Author: FL <Friedrich.Leisch@ci.tuwien.ac.at>
## Description: Apply Spencer's 15-point MA filter
function retval = spencer (x)
if (nargin != 1)
print_usage ();
endif
[xr, xc] = size (x);
n = xr;
c = xc;
if (isvector (x))
n = length (x);
c = 1;
x = reshape (x, n, 1);
endif
w = [-3, -6, -5, 3, 21, 46, 67, 74, 67, 46, 21, 3, -5, -6, -3] / 320;
retval = fftfilt (w, x);
retval = [zeros(7,c); retval(15:n,:); zeros(7,c);];
retval = reshape (retval, xr, xc);
endfunction
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