Mercurial > hg > octave-nkf
view scripts/signal/fftshift.m @ 15536:2e8eb9ac43a5 stable rc-3-6-4-0
3.6.4-rc0 release candidate
* configure.ac (AC_INIT): Version is now 3.6.2-rc0.
(OCTAVE_RELEASE_DATE): Now 2012-05-11.
author | John W. Eaton <jwe@octave.org> |
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date | Wed, 17 Oct 2012 10:05:44 -0400 |
parents | 72c96de7a403 |
children | f3d52523cde1 |
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## Copyright (C) 1997-2012 Vincent Cautaerts ## ## 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 3 of the License, 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, see ## <http://www.gnu.org/licenses/>. ## -*- texinfo -*- ## @deftypefn {Function File} {} fftshift (@var{x}) ## @deftypefnx {Function File} {} fftshift (@var{x}, @var{dim}) ## Perform a shift of the vector @var{x}, for use with the @code{fft} ## and @code{ifft} functions, in order the move the frequency 0 to the ## center of the vector or matrix. ## ## If @var{x} is a vector of @math{N} elements corresponding to @math{N} ## time samples spaced by @math{dt}, then ## @code{fftshift (fft (@var{x}))} corresponds to frequencies ## ## @example ## f = [ -(ceil((N-1)/2):-1:1)*df 0 (1:floor((N-1)/2))*df ] ## @end example ## ## @noindent ## where @nospell{@math{df}} = 1 / @math{dt}. ## ## If @var{x} is a matrix, the same holds for rows and columns. If ## @var{x} is an array, then the same holds along each dimension. ## ## The optional @var{dim} argument can be used to limit the dimension ## along which the permutation occurs. ## @end deftypefn ## Author: Vincent Cautaerts <vincent@comf5.comm.eng.osaka-u.ac.jp> ## Created: July 1997 ## Adapted-By: jwe function retval = fftshift (x, dim) if (nargin != 1 && nargin != 2) print_usage (); endif if (nargin == 2) if (! (isscalar (dim) && dim > 0 && dim == fix (dim))) error ("fftshift: dimension DIM must be a positive integer"); endif nd = ndims (x); sz = size (x); sz2 = ceil (sz(dim) / 2); idx = cell (); idx = repmat ({':'}, nd, 1); idx{dim} = [sz2+1:sz(dim), 1:sz2]; retval = x(idx{:}); else if (isvector (x)) xl = length (x); xx = ceil (xl/2); retval = x([xx+1:xl, 1:xx]); elseif (ismatrix (x)) nd = ndims (x); sz = size (x); sz2 = ceil (sz ./ 2); idx = cell (); for i = 1:nd idx{i} = [sz2(i)+1:sz(i), 1:sz2(i)]; endfor retval = x(idx{:}); else error ("fftshift: expecting vector or matrix argument"); endif endif endfunction %!test %! x = [0:7]; %! y = fftshift (x); %! assert(y, [4 5 6 7 0 1 2 3]); %! assert(fftshift (y), x); %!test %! x = [0:6]; %! y = fftshift (x); %! assert(y, [4 5 6 0 1 2 3]); %! assert(fftshift (y), [1 2 3 4 5 6 0]); %!test %! x = [0:7]'; %! y = fftshift (x); %! assert(y, [4;5;6;7;0;1;2;3]); %! assert(fftshift (y), x); %!test %! x = [0:6]'; %! y = fftshift (x); %! assert(y, [4;5;6;0;1;2;3]); %! assert(fftshift (y), [1;2;3;4;5;6;0]); %!test %! x = [0:3]; %! x = [x;2*x;3*x+1;4*x+1]; %! y = fftshift (x); %! assert(y, [[7 10 1 4];[9 13 1 5];[2 3 0 1];[4 6 0 2]]); %! assert(fftshift (y), x); %!test %! x = [0:3]; %! x = [x;2*x;3*x+1;4*x+1]; %! y = fftshift (x,1); %! assert(y, [[1 4 7 10];[1 5 9 13];[0 1 2 3];[0 2 4 6]]); %! assert(fftshift (y,1), x); %!test %! x = [0:3]; %! x = [x;2*x;3*x+1;4*x+1]; %! y = fftshift (x,2); %! assert(y, [[2 3 0 1];[4 6 0 2];[7 10 1 4];[9 13 1 5]]); %! assert(fftshift (y,2), x);