1 ## Copyright (C) 1994-2012 John W. Eaton
3 ## This file is part of Octave.
5 ## Octave is free software; you can redistribute it and/or modify it
6 ## under the terms of the GNU General Public License as published by
7 ## the Free Software Foundation; either version 3 of the License, or (at
8 ## your option) any later version.
10 ## Octave is distributed in the hope that it will be useful, but
11 ## WITHOUT ANY WARRANTY; without even the implied warranty of
12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 ## General Public License for more details.
15 ## You should have received a copy of the GNU General Public License
16 ## along with Octave; see the file COPYING. If not, see
17 ## <http://www.gnu.org/licenses/>.
20 ## @deftypefn {Function File} {} fftfilt (@var{b}, @var{x}, @var{n})
22 ## With two arguments, @code{fftfilt} filters @var{x} with the FIR filter
23 ## @var{b} using the FFT.
25 ## Given the optional third argument, @var{n}, @code{fftfilt} uses the
26 ## overlap-add method to filter @var{x} with @var{b} using an N-point FFT.
28 ## If @var{x} is a matrix, filter each column of the matrix.
29 ## @seealso{filter, filter2}
32 ## Author: Kurt Hornik <Kurt.Hornik@wu-wien.ac.at>
33 ## Created: 3 September 1994
36 function y = fftfilt (b, x, n)
38 ## If N is not specified explicitly, we do not use the overlap-add
39 ## method at all because loops are really slow. Otherwise, we only
40 ## ensure that the number of points in the FFT is the smallest power
41 ## of two larger than N and length(b). This could result in length
42 ## one blocks, but if the user knows better ...
44 if (nargin < 2 || nargin > 3)
48 transpose = (rows (x) == 1);
54 [r_x, c_x] = size (x);
55 [r_b, c_b] = size (b);
58 error ("fftfilt: B must be a vector");
62 error ("fftfilt: X must be a 1-D or 2-D array");
66 b = reshape (b, l_b, 1);
69 ## Use FFT with the smallest power of 2 which is >= length (x) +
70 ## length (b) - 1 as number of points ...
71 n = 2 ^ nextpow2 (r_x + l_b - 1);
73 y = ifft (fft (x, n) .* B(:, ones (1, c_x)));
75 ## Use overlap-add method ...
77 error ("fftfilt: N has to be a scalar");
79 n = 2 ^ nextpow2 (max ([n, l_b]));
82 B = B(:, ones (c_x,1));
87 hi = min (r * L, r_x);
89 tmp(1:(hi-lo+1),:) = x(lo:hi,:);
90 tmp = ifft (fft (tmp) .* B);
91 hi = min (lo+n-1, r_x);
92 y(lo:hi,:) = y(lo:hi,:) + tmp(1:(hi-lo+1),:);
101 ## Final cleanups: If both x and b are real, y should be real.
102 ## If both x and b are integer, y should be integer.
104 if (isreal (b) && isreal (x))
107 if (! any (b - fix (b)))
108 idx = !any (x - fix (x));
109 y(:, idx) = round (y(:, idx));
118 %! x = [1, zeros(1,9)];
119 %! assert(fftfilt(b, x ), [1 1 0 0 0 0 0 0 0 0] , eps);
120 %! assert(fftfilt(b, x.'), [1 1 0 0 0 0 0 0 0 0].', eps);
121 %! assert(fftfilt(b.',x ), [1 1 0 0 0 0 0 0 0 0] , eps);
122 %! assert(fftfilt(b.',x.'), [1 1 0 0 0 0 0 0 0 0].', eps);
125 %! r = sqrt(1/2) * (1+i);
127 %! assert(fftfilt(b, x ), r*[1 1 0 0 0 0 0 0 0 0] , eps);
128 %! assert(fftfilt(b, r*x), r*r*[1 1 0 0 0 0 0 0 0 0], eps);
129 %! assert(fftfilt(b, x.'), r*[1 1 0 0 0 0 0 0 0 0].', eps);
133 %! x = zeros (10,3); x(1,1)=-1; x(1,2)=1;
134 %! y0 = zeros (10,3); y0(1:2,1)=-1; y0(1:2,2)=1;
135 %! y = fftfilt (b, x);
141 %! y0 = filter (b, 1, x);
142 %! y = filter (b, 1, x);
145 %% Test input validation
147 %!error fftfilt (1, 2, 3, 4)
148 %!error fftfilt (ones (2), 1)
149 %!error fftfilt (2, ones (3,3,3))
150 %!error fftfilt (2, 1, ones (2))