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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, 59 Temple Place - Suite 330, Boston, MA |
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18 ## 02111-1307, 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 ## Perform a shift of the vector @var{v}, for use with the @code{fft} |
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23 ## and @code{ifft} functions, in order the move the frequency 0 to the |
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24 ## center of the vector or matrix. |
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25 ## |
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26 ## If @var{v} is a vector of @math{E} elements corresponding to @math{E} |
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27 ## time samples spaced of @math{Dt} each, then @code{fftshift (fft |
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28 ## (@var{v}))} corresponds to frequencies |
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29 ## |
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30 ## @example |
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31 ## f = linspace (-E/(4*Dt), (E/2-1)/(2*Dt), E) |
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32 ## @end example |
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33 ## |
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34 ## If @var{v} is a matrix, the same holds for rows and columns. |
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35 ## @end deftypefn |
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36 |
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37 ## Author: Vincent Cautaerts <vincent@comf5.comm.eng.osaka-u.ac.jp> |
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38 ## Created: July 1997 |
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39 ## Adapted-By: jwe |
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40 |
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41 function retval = fftshift (V) |
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42 |
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43 retval = 0; |
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44 |
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45 if (nargin != 1) |
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46 usage ("usage: fftshift (X)"); |
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47 endif |
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48 |
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49 if (is_vector (V)) |
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50 x = length (V); |
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51 xx = ceil (x/2); |
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52 retval = V([xx+1:x, 1:xx]); |
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53 elseif (is_matrix (V)) |
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54 [x, y] = size (V); |
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55 xx = ceil (x/2); |
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56 yy = ceil (y/2); |
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57 retval = V([xx+1:x, 1:xx], [yy+1:y, 1:yy]); |
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58 else |
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59 error ("fftshift: expecting vector or matrix argument"); |
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60 endif |
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61 |
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62 endfunction |
