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## Copyright (C) 1995, 1996, 1997 Friedrich Leisch
##
## 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 2, 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 file. If not, write to the Free Software Foundation,
## 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
## usage: spencer (X)
##
## returns Spencer's 15 point moving average of every single column of X
## Author: FL <Friedrich.Leisch@ci.tuwien.ac.at>
## Description: Apply Spencer's 15-point MA filter
function retval = spencer (X)
if (nargin != 1)
usage ("spencer (X)");
endif
[xr, xc] = size(X);
n = xr;
c = xc;
if (is_vector(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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