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scripts/signal/fftshift.m

changeset 10289: 4b124317dc38
parent:eb63fbe60fab
author: John W. Eaton <jwe@octave.org>
date: Tue Feb 09 20:58:55 2010 -0500 (59 minutes ago)
permissions: -rw-r--r--
description: base_properties::set_children: account for hidden children 
     1## Copyright (C) 1997, 1998, 2000, 2002, 2004, 2005, 2006, 2007, 2009

     2##               Vincent Cautaerts

     3##

     4## This file is part of Octave.

     5##

     6## Octave is free software; you can redistribute it and/or modify it

     7## under the terms of the GNU General Public License as published by

     8## the Free Software Foundation; either version 3 of the License, or (at

     9## your option) any later version.

    10##

    11## Octave is distributed in the hope that it will be useful, but

    12## WITHOUT ANY WARRANTY; without even the implied warranty of

    13## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

    14## General Public License for more details.

    15##

    16## You should have received a copy of the GNU General Public License

    17## along with Octave; see the file COPYING.  If not, see

    18## <http://www.gnu.org/licenses/>.

    19

    20## -*- texinfo -*-

    21## @deftypefn {Function File} {} fftshift (@var{v})

    22## @deftypefnx {Function File} {} fftshift (@var{v}, @var{dim})

    23## Perform a shift of the vector @var{v}, for use with the @code{fft}

    24## and @code{ifft} functions, in order the move the frequency 0 to the

    25## center of the vector or matrix.

    26##

    27## If @var{v} is a vector of @math{N} elements corresponding to @math{N}

    28## time samples spaced of @math{Dt} each, then @code{fftshift (fft

    29## (@var{v}))} corresponds to frequencies

    30##

    31## @example

    32## f = ((1:N) - ceil(N/2)) / N / Dt

    33## @end example

    34##

    35## If @var{v} is a matrix, the same holds for rows and columns.  If 

    36## @var{v} is an array, then the same holds along each dimension.

    37##

    38## The optional @var{dim} argument can be used to limit the dimension

    39## along which the permutation occurs.

    40## @end deftypefn

    41

    42## Author: Vincent Cautaerts <vincent@comf5.comm.eng.osaka-u.ac.jp>

    43## Created: July 1997

    44## Adapted-By: jwe

    45

    46function retval = fftshift (V, dim)

    47

    48  retval = 0;

    49

    50  if (nargin != 1 && nargin != 2)

    51    print_usage ();

    52  endif

    53

    54  if (nargin == 2)

    55    if (!isscalar (dim))

    56      error ("fftshift: dimension must be an integer scalar");

    57    endif

    58    nd = ndims (V);

    59    sz = size (V);

    60    sz2 = ceil (sz(dim) / 2);

    61    idx = cell ();

    62    for i = 1:nd

    63      idx{i} = 1:sz(i);

    64    endfor

    65    idx{dim} = [sz2+1:sz(dim), 1:sz2];

    66    retval = V (idx{:});

    67  else

    68    if (isvector (V))

    69      x = length (V);

    70      xx = ceil (x/2);

    71      retval = V([xx+1:x, 1:xx]);

    72    elseif (ismatrix (V))

    73      nd = ndims (V);

    74      sz = size (V);

    75      sz2 = ceil (sz ./ 2);

    76      idx = cell ();

    77      for i = 1:nd

    78        idx{i} = [sz2(i)+1:sz(i), 1:sz2(i)];

    79      endfor

    80      retval = V (idx{:});

    81    else

    82      error ("fftshift: expecting vector or matrix argument");

    83    endif

    84  endif

    85

    86endfunction