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1 ## Copyright (C) 1995, 1996 Kurt Hornik |
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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 {Mapping Function} {} log2 (@var{x}) |
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22 ## @deftypefnx {Mapping Function} {[@var{f}, @var{e}] =} log2 (@var{x}) |
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23 ## Compute the base-2 logarithm of @var{x}. With two outputs, returns |
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24 ## @var{f} and @var{e} such that |
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25 ## @iftex |
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26 ## @tex |
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27 ## $1/2 <= |f| < 1$ and $x = f \cdot 2^e$. |
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28 ## @end tex |
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29 ## @end iftex |
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30 ## @ifinfo |
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31 ## 1/2 <= abs(f) < 1 and x = f * 2^e. |
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32 ## @end ifinfo |
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33 ## @end deftypefn |
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34 ## |
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35 ## @seealso{log, log10, logspace, and exp} |
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36 |
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37 ## Author: AW <Andreas.Weingessel@ci.tuwien.ac.at> |
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38 ## Created: 17 October 1994 |
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39 ## Adapted-By: jwe |
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40 |
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41 function [f, e] = log2 (x) |
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42 |
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43 if (nargin != 1) |
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44 usage ("y = log2 (x) or [f, e] = log2 (x)"); |
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45 endif |
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46 |
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47 if (nargout < 2) |
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48 f = log (x) / log (2); |
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49 elseif (nargout == 2) |
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50 ## Only deal with the real parts ... |
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51 x = real (x); |
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52 ## Since log (0) gives problems, 0 entries are replaced by 1. |
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53 ## This is corrected later by multiplication with the sign. |
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54 f = abs (x) + (x == 0); |
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55 e = (floor (log (f) / log (2)) + 1) .* (x != 0); |
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56 f = sign (x) .* f ./ (2 .^ e); |
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57 else |
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58 error ("log2 takes at most 2 output arguments"); |
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59 endif |
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60 |
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61 endfunction |
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62 |
