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1 ## Copyright (C) 1995, 1996 Kurt Hornik |
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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 ## -*- texinfo -*- |
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18 ## @deftypefn {Function File} {} diff (@var{x}, @var{k}) |
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19 ## If @var{x} is a vector of length @var{n}, @code{diff (@var{x})} is the |
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20 ## vector of first differences |
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21 ## @iftex |
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22 ## @tex |
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23 ## $x_2 - x_1, \ldots{}, x_n - x_{n-1}$. |
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24 ## @end tex |
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25 ## @end iftex |
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26 ## @ifinfo |
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27 ## @var{x}(2) - @var{x}(1), @dots{}, @var{x}(n) - @var{x}(n-1). |
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28 ## @end ifinfo |
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29 ## |
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30 ## If @var{x} is a matrix, @code{diff (@var{x})} is the matrix of column |
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31 ## differences. |
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32 ## |
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33 ## The second argument is optional. If supplied, @code{diff (@var{x}, |
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34 ## @var{k})}, where @var{k} is a nonnegative integer, returns the |
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35 ## @var{k}-th differences. |
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36 ## @end deftypefn |
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37 |
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38 ## Author: KH <Kurt.Hornik@ci.tuwien.ac.at> |
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39 ## Created: 2 February 1995 |
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40 ## Adapted-By: jwe |
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41 |
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42 function x = diff (x, k) |
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43 |
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44 if (nargin == 1) |
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45 k = 1; |
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46 elseif (nargin == 2) |
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47 if (! (is_scalar (k) && k == round (k) && k >= 0)) |
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48 error ("diff: k must be a nonnegative integer"); |
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49 elseif (k == 0) |
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50 return; |
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51 endif |
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52 else |
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53 usage ("diff (x [, k]"); |
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54 endif |
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55 |
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56 if (isstr (x)) |
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57 error ("diff: symbolic differentiation not (yet) supported"); |
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58 elseif (is_vector (x)) |
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59 n = length (x); |
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60 if (n <= k) |
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61 x = []; |
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62 else |
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63 for i = 1 : k |
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64 x = x (2 : (n - i + 1)) - x (1 : (n - i)); |
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65 endfor |
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66 endif |
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67 elseif (is_matrix (x)) |
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68 n = rows (x); |
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69 if (n <= k) |
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70 x = []; |
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71 else |
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72 for i = 1 : k |
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73 x = x (2 : (n - i + 1), :) - x (1: (n - i), :); |
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74 endfor |
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75 endif |
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76 else |
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77 x = []; |
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78 endif |
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79 |
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80 endfunction |
