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1 ## Copyright (C) 1996, 1997 John W. Eaton |
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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} {} sinc (@var{x}) |
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22 ## Return |
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23 ## @iftex |
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24 ## @tex |
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25 ## $ \sin (\pi x)/(\pi x)$. |
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26 ## @end tex |
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27 ## @end iftex |
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28 ## @ifinfo |
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29 ## sin(pi*x)/(pi*x). |
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30 ## @end ifinfo |
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31 ## @end deftypefn |
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32 |
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33 ## Author: jwe ??? |
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34 |
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35 function result = sinc (x) |
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36 |
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37 ## We either need to set the do_fortran_indexing variable to "true" |
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38 ## or use reshape to convert the input matrix to a vector, so that |
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39 ## we can use find to determine the elements of x that equal zero. |
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40 ## I prefer reshaping. |
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41 |
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42 [nr, nc] = size(x); |
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43 |
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44 nels = nr*nc; |
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45 |
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46 x = reshape(x,nels,1); |
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47 |
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48 ## Set result to all ones initially. |
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49 result = ones(nels,1); |
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50 |
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51 ## Find non-zero elements in the input matrix. |
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52 i = find(x); |
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53 |
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54 if (!isempty(i)) |
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55 result(i) = sin(pi*x(i))./(pi*x(i)); |
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56 endif |
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57 |
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58 result = reshape(result,nr,nc); |
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59 |
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60 endfunction |
