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1 # Copyright (C) 1993, 1994, 1995 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 the |
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7 # Free Software Foundation; either version 2, or (at your option) any |
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8 # later version. |
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9 # |
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10 # Octave is distributed in the hope that it will be useful, but WITHOUT |
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11 # ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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12 # FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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13 # 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 02111-1307, USA. |
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18 |
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19 function retval = std (a) |
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20 |
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21 # usage: std (a) |
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22 # |
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23 # For vector arguments, std returns the standard deviation of the |
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24 # values. For matrix arguments, std returns a row vector containing |
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25 # the standard deviation for each column. |
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26 # |
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27 # See also: mean, median |
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28 |
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29 if (nargin != 1) |
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30 usage ("std (a)"); |
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31 endif |
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32 |
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33 nr = rows (a); |
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34 nc = columns (a); |
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35 if (nc == 1 && nr == 1) |
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36 retval = 0; |
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37 elseif (nc == 1 || nr == 1) |
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38 tmp = sum (a); |
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39 n = length (a); |
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40 retval = sqrt ((n * sumsq (a) - tmp .* tmp) / (n * (n - 1))); |
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41 elseif (nr > 1 && nc > 0) |
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42 tmp = sum (a); |
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43 retval = sqrt ((nr * sumsq (a) - tmp .* tmp) / (nr * (nr - 1))); |
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44 else |
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45 error ("mean: invalid matrix argument"); |
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46 endif |
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47 |
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48 endfunction |
