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annotate scripts/signal/fftshift.m @ 3191:e4f4b2d26ee9

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[project @ 1998-10-23 05:43:59 by jwe]
author jwe
date Fri, 23 Oct 1998 05:44:01 +0000
parents
children f8dde1807dee
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1 ## Copyright (C) 1997 by Vincent Cautaerts
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2 ##
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3 ## This program is free software; you can redistribute it and/or modify
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4 ## it under the terms of the GNU General Public License as published by
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5 ## the Free Software Foundation; either version 2, or (at your option)
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6 ## any later version.
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7 ##
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8 ## This program is distributed in the hope that it will be useful, but
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9 ## WITHOUT ANY WARRANTY; without even the implied warranty of
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10 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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11 ## General Public License for more details.
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12 ##
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13 ## You should have received a copy of the GNU General Public License
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14 ## along with this file. If not, write to the Free Software Foundation,
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15 ## 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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16
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17 ## usage: y = fftshift(W)
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18 ##
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19 ## Performs a shift of the vector V, for use with the "fft" and "ifft"
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20 ## functions, in order the move the frequency 0 to the centre of
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21 ## the vector or matrix.
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22 ##
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23 ## If V is a vector of E datas corresponding to E time samples spaced
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24 ## of Dt each, then fftshift (fft (V)) correspond to frequencies
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25 ##
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26 ## f = linspace (-E/(4*DT), (E/2-1)/(2*DT), E)
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27 ##
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28 ## If V is a matrix, does the same holds for rows and columns.
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29
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30 ## Author: Vincent Cautaerts <vincent@comf5.comm.eng.osaka-u.ac.jp>
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31 ## Created: July 1997
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32 ## Adapted-By: jwe
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33
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34 function retval = fftshift (V)
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35
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36 retval = 0;
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37
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38 if (nargin != 1)
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39 usage ("usage: fftshift (X)");
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40 endif
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41
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42 if (is_vector (V))
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43 x = length (V);
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44 xx = ceil (x/2);
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45 retval = V([xx+1:x, 1:xx]);
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46 elseif (is_matrix (V))
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47 [x, y] = size (V);
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48 xx = ceil (x/2);
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49 yy = ceil (y/2);
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50 retval = V([xx+1:x, 1:xx], [yy+1:y, 1:yy]);
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51 else
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52 error ("fftshift: expecting vector or matrix argument");
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53 endif
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54
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55 endfunction