1 ## Copyright (C) 1995-2012 Friedrich Leisch
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.
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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
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20 ## @deftypefn {Function File} {} fractdiff (@var{x}, @var{d})
21 ## Compute the fractional differences @math{(1-L)^d x} where @math{L}
22 ## denotes the lag-operator and @math{d} is greater than -1.
25 ## Author: FL <Friedrich.Leisch@ci.tuwien.ac.at>
26 ## Description: Compute fractional differences
28 function retval = fractdiff (x, d)
37 error ("fractdiff: X must be a vector");
41 error ("fractdiff: D must be a scalar");
47 x = x(2 : length (x)) - x(1 : length (x) - 1);
57 w = real (gamma (-d+n) ./ gamma (-d) ./ gamma (n+1));
58 retval = fftfilt (w, x);
59 retval = retval(1 : length (x));
65 error ("fractdiff: D must be > -1");