1 ## Copyright (C) 1995-2012 Kurt Hornik
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} {} detrend (@var{x}, @var{p})
21 ## If @var{x} is a vector, @code{detrend (@var{x}, @var{p})} removes the
22 ## best fit of a polynomial of order @var{p} from the data @var{x}.
24 ## If @var{x} is a matrix, @code{detrend (@var{x}, @var{p})} does the same
25 ## for each column in @var{x}.
27 ## The second argument is optional. If it is not specified, a value of 1
28 ## is assumed. This corresponds to removing a linear trend.
30 ## The order of the polynomial can also be given as a string, in which case
31 ## @var{p} must be either @t{"constant"} (corresponds to @code{@var{p}=0}) or
32 ## @t{"linear"} (corresponds to @code{@var{p}=1}).
36 ## Author: KH <Kurt.Hornik@wu-wien.ac.at>
37 ## Created: 11 October 1994
40 function y = detrend (x, p = 1)
42 if (nargin > 0 && isreal (x) && ndims (x) <= 2)
44 if (ischar (p) && strcmpi (p, "constant"))
46 elseif (ischar (p) && strcmpi (p, "linear"))
48 elseif (!isscalar (p) || p < 0 || p != fix (p))
49 error ("detrend: second input argument must be 'constant', 'linear' or a positive integer");
52 error ("detrend: first input argument must be a real vector or matrix");
61 b = ((1 : r)' * ones (1, p + 1)) .^ (ones (r, 1) * (0 : p));
72 %! x = (0:1:N-1)/N + 2;
74 %! assert(all (all (abs (y) < 20*eps)));
81 %! assert(all (all (abs (y) < 30*eps)));
88 %! assert(all (all (abs (y) < 20*eps)));