Mercurial > octave-nkf
view scripts/signal/fftshift.m @ 3449:858695b3ed62
[project @ 2000-01-18 04:08:59 by jwe]
author | jwe |
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date | Tue, 18 Jan 2000 04:09:14 +0000 |
parents | f8dde1807dee |
children | 3e3e14ad5149 |
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## Copyright (C) 1997 by Vincent Cautaerts ## ## This program 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. ## ## This program 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 this file. If not, write to the Free Software Foundation, ## 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. ## -*- texinfo -*- ## @deftypefn {Function File} {} fftshift (@var{v}) ## Perform a shift of the vector @var{v}, for use with the @code{fft} ## and @code{ifft} functions, in order the move the frequency 0 to the ## centre of the vector or matrix. ## ## If @var{v} is a vector of @var{E} elements corresponding to @var{E} ## time samples spaced of @var{Dt} each, then @code{fftshift (fft ## (@var{v}))} corresponds to frequencies ## ## @example ## f = linspace (-@var{E}/(4*@var{Dt}), (@var{E}/2-1)/(2*@var{Dt}), @var{E}) ## @end example ## ## If @var{v} is a matrix, does the same holds for rows and columns. ## @end deftypefn ## Author: Vincent Cautaerts <vincent@comf5.comm.eng.osaka-u.ac.jp> ## Created: July 1997 ## Adapted-By: jwe function retval = fftshift (V) retval = 0; if (nargin != 1) usage ("usage: fftshift (X)"); endif if (is_vector (V)) x = length (V); xx = ceil (x/2); retval = V([xx+1:x, 1:xx]); elseif (is_matrix (V)) [x, y] = size (V); xx = ceil (x/2); yy = ceil (y/2); retval = V([xx+1:x, 1:xx], [yy+1:y, 1:yy]); else error ("fftshift: expecting vector or matrix argument"); endif endfunction