## Copyright (C) 1996, 1997 John W. Eaton ## ## 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 2, 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, write to the Free ## Software Foundation, 59 Temple Place - Suite 330, Boston, MA ## 02111-1307, USA. ## -*- texinfo -*- ## @deftypefn {Function File} {} fftfilt (@var{b}, @var{x}, @var{n}) ## ## With two arguments, @code{fftfilt} filters @var{x} with the FIR filter ## @var{b} using the FFT. ## ## Given the optional third argument, @var{n}, @code{fftfilt} uses the ## overlap-add method to filter @var{x} with @var{b} using an N-point FFT. ## ## If @var{x} is a matrix, filter each column of the matrix. ## @end deftypefn ## Author: KH <Kurt.Hornik@ci.tuwien.ac.at> ## Created: 3 September 1994 ## Adapted-By: jwe ## Paul Kienzle <pkienzle@kienzle.powernet.co.uk> ## handle matrices function y = fftfilt (b, x, N) ## If N is not specified explicitly, we do not use the overlap-add ## method at all because loops are really slow. Otherwise, we only ## ensure that the number of points in the FFT is the smallest power ## of two larger than N and length(b). This could result in length ## one blocks, but if the user knows better ... if (nargin < 2 || nargin > 3) usage (" fftfilt (b, x, N)"); endif transpose = rows(x) == 1; if transpose, x = x.'; endif [r_x, c_x] = size (x); [r_b, c_b] = size (b); if min ([r_b, c_b]) != 1 error ("fftfilt: b should be a vector"); endif l_b = r_b * c_b; b = reshape (b, l_b, 1); if (nargin == 2) ## Use FFT with the smallest power of 2 which is >= length (x) + ## length (b) - 1 as number of points ... N = 2^(ceil (log (r_x + l_b - 1) / log(2))); B = fft (b, N); y = ifft(fft (x, N) .* B(:,ones(1,c_x))); else ## Use overlap-add method ... if (! (is_scalar (N))) error ("fftfilt: N has to be a scalar"); endif N = 2^(ceil (log (max ([N, l_b])) / log(2))); L = N - l_b + 1; B = fft (b, N); R = ceil (r_x / L); y = zeros (r_x, c_x); for r = 1:R; lo = (r - 1) * L + 1; hi = min (r * L, r_x); tmp = zeros(N,c_x); tmp(1:(hi-lo+1),:) = x(lo:hi,:); tmp = ifft(fft (tmp) .* B(:,ones(c_x,1))); hi = min (lo+N-1, r_x); y(lo:hi,:) = y(lo:hi,:) + tmp(1:(hi-lo+1),:); endfor endif y = y(1:r_x,:); if transpose, y=y.'; endif ## Final cleanups: if both x and b are real respectively integer, y ## should also be if (! (any (imag (x)) || any (imag (b)))) y = real (y); endif if (! (any (x - round (x)) || any (b - round (b)))) y = round (y); endif endfunction

Generated by Doxygen 1.6.0 Back to index