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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 ## usage: diff (x [, k]) |
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18 ## |
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19 ## If x is a vector of length n, diff (x) is the vector of first |
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20 ## differences x(2) - x(1), ..., x(n) - x(n-1). |
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21 ## |
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22 ## If x is a matrix, diff (x) is the matrix of column differences. |
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23 ## diff (x, k), where k is a nonnegative integer, returns the k-th |
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24 ## differences. |
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25 |
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26 ## Author: KH <Kurt.Hornik@ci.tuwien.ac.at> |
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27 ## Created: 2 February 1995 |
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28 ## Adapted-By: jwe |
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29 |
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30 function x = diff (x, k) |
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31 |
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32 if (nargin == 1) |
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33 k = 1; |
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34 elseif (nargin == 2) |
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35 if (! (is_scalar (k) && k == round (k) && k >= 0)) |
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36 error ("diff: k must be a nonnegative integer"); |
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37 elseif (k == 0) |
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38 return; |
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39 endif |
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40 else |
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41 usage ("diff (x [, k]"); |
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42 endif |
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43 |
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44 if (isstr (x)) |
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45 error ("diff: symbolic differentiation not (yet) supported"); |
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46 elseif (is_vector (x)) |
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47 n = length (x); |
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48 if (n <= k) |
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49 x = []; |
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50 else |
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51 for i = 1 : k |
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52 x = x (2 : (n - i + 1)) - x (1 : (n - i)); |
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53 endfor |
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54 endif |
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55 elseif (is_matrix (x)) |
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56 n = rows (x); |
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57 if (n <= k) |
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58 x = []; |
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59 else |
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60 for i = 1 : k |
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61 x = x (2 : (n - i + 1), :) - x (1: (n - i), :); |
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62 endfor |
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63 endif |
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64 else |
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65 x = []; |
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66 endif |
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67 |
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68 endfunction |
