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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} {} std (@var{x}) |
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22 ## If @var{x} is a vector, compute the standard deviation of the elements |
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23 ## of @var{x}. |
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24 ## @iftex |
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25 ## @tex |
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26 ## $$ |
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27 ## {\rm std} (x) = \sigma (x) = \sqrt{{\sum_{i=1}^N (x_i - \bar{x}) \over N - 1}} |
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28 ## $$ |
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29 ## @end tex |
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30 ## @end iftex |
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31 ## @ifinfo |
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32 ## |
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33 ## @example |
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34 ## @group |
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35 ## std (x) = sqrt (sumsq (x - mean (x)) / (n - 1)) |
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36 ## @end group |
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37 ## @end example |
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38 ## @end ifinfo |
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39 ## If @var{x} is a matrix, compute the standard deviation for |
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40 ## each column and return them in a row vector. |
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41 ## @end deftypefn |
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42 ## @seealso{mean and median} |
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43 |
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44 ## Author: jwe |
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45 |
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46 function retval = std (a) |
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47 |
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48 if (nargin != 1) |
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49 usage ("std (a)"); |
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50 endif |
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51 |
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52 nr = rows (a); |
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53 nc = columns (a); |
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54 if (nc == 1 && nr == 1) |
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55 retval = 0; |
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56 elseif (nc == 1 || nr == 1) |
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57 n = length (a); |
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58 retval = sqrt (sumsq (a - mean (a)) / (n - 1)); |
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59 elseif (nr > 1 && nc > 0) |
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60 retval = sqrt (sumsq (a - ones (nr, 1) * mean (a)) / (nr - 1)); |
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61 else |
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62 error ("std: invalid matrix argument"); |
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63 endif |
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64 |
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65 endfunction |
