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1 ## Copyright (C) 1997 by Vincent Cautaerts |
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2 ## |
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3 ## This file is part of Octave. |
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4 ## |
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5 ## Octave is free software; you can redistribute it and/or modify it |
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6 ## under the terms of the GNU General Public License as published by |
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7 ## the Free Software Foundation; either version 2, or (at your option) |
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8 ## any later version. |
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9 ## |
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10 ## Octave is distributed in the hope that it will be useful, but |
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11 ## WITHOUT ANY WARRANTY; without even the implied warranty of |
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12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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13 ## General Public License for more details. |
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14 ## |
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15 ## You should have received a copy of the GNU General Public License |
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16 ## along with Octave; see the file COPYING. If not, write to the Free |
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17 ## Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA |
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18 ## 02110-1301, USA. |
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19 |
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20 ## -*- texinfo -*- |
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21 ## @deftypefn {Function File} {} fftshift (@var{v}) |
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22 ## @deftypefnx {Function File} {} fftshift (@var{v}, @var{dim}) |
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23 ## Perform a shift of the vector @var{v}, for use with the @code{fft} |
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24 ## and @code{ifft} functions, in order the move the frequency 0 to the |
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25 ## center of the vector or matrix. |
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26 ## |
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27 ## If @var{v} is a vector of @math{N} elements corresponding to @math{N} |
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28 ## time samples spaced of @math{Dt} each, then @code{fftshift (fft |
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29 ## (@var{v}))} corresponds to frequencies |
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30 ## |
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31 ## @example |
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32 ## f = ((1:N) - ceil(N/2)) / N / Dt |
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33 ## @end example |
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34 ## |
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35 ## If @var{v} is a matrix, the same holds for rows and columns. If |
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36 ## @var{v} is an array, then the same holds along each dimension. |
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37 ## |
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38 ## The optional @var{dim} argument can be used to limit the dimension |
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39 ## along which the permutation occurs. |
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40 ## @end deftypefn |
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41 |
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42 ## Author: Vincent Cautaerts <vincent@comf5.comm.eng.osaka-u.ac.jp> |
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43 ## Created: July 1997 |
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44 ## Adapted-By: jwe |
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45 |
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46 function retval = fftshift (V, dim) |
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47 |
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48 retval = 0; |
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49 |
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50 if (nargin != 1 && nargin != 2) |
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51 usage ("usage: fftshift (X, dim)"); |
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52 endif |
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53 |
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54 if (nargin == 2) |
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55 if (!isscalar (dim)) |
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56 error ("fftshift: dimension must be an integer scalar"); |
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57 endif |
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58 nd = ndims (V); |
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59 sz = size (V); |
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60 sz2 = ceil (sz(dim) / 2); |
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61 idx = cell (); |
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62 for i=1:nd |
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63 idx {i} = 1:sz(i); |
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64 endfor |
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65 idx {dim} = [sz2+1:sz(dim), 1:sz2]; |
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66 retval = V (idx{:}); |
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67 else |
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68 if (isvector (V)) |
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69 x = length (V); |
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70 xx = ceil (x/2); |
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71 retval = V([xx+1:x, 1:xx]); |
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72 elseif (ismatrix (V)) |
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73 nd = ndims (V); |
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74 sz = size (V); |
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75 sz2 = ceil (sz ./ 2); |
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76 idx = cell (); |
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77 for i=1:nd |
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78 idx{i} = [sz2(i)+1:sz(i), 1:sz2(i)]; |
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79 endfor |
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80 retval = V (idx{:}); |
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81 else |
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82 error ("fftshift: expecting vector or matrix argument"); |
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83 endif |
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84 endif |
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85 |
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86 endfunction |
