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isprime: produce logical result
author John W. Eaton <jwe@octave.org>
date Mon, 14 Dec 2009 13:50:11 -0500
parents f084ba47812b
children c6833d31f34e
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1 ## Copyright (C) 2000, 2006, 2007, 2009 Paul Kienzle
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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 3 of the License, or (at
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8 ## your option) 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, see
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17 ## <http://www.gnu.org/licenses/>.
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18
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19 ## -*- texinfo -*-
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20 ## @deftypefn {Function File} {} isprime (@var{n})
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21 ## Return true if @var{n} is a prime number, false otherwise.
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22 ##
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23 ## Something like the following is much faster if you need to test a lot
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24 ## of small numbers:
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25 ##
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26 ## @example
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27 ## @var{t} = ismember (@var{n}, primes (max (@var{n} (:))));
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28 ## @end example
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29 ##
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30 ## If max(n) is very large, then you should be using special purpose
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31 ## factorization code.
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32 ##
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33 ## @seealso{primes, factor, gcd, lcm}
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34 ## @end deftypefn
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35
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36 function t = isprime (n)
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37
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38 if (nargin == 1)
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39 if (! isscalar (n))
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40 nel = numel (n);
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41 t = zeros (size (n), "logical");
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42 for i = 1:nel
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43 t(i) = isprime (n(i));
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44 endfor
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45 elseif (n != fix (n) || n < 2)
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46 t = logical (0);
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47 elseif (n < 9)
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48 t = all (n != [4, 6, 8]);
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49 else
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50 q = n./[2, 3:2:sqrt(n)];
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51 t = all (q != fix (q));
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52 endif
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53 else
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54 print_usage ();
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55 endif
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56
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57 endfunction
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58
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59 %!assert (isprime (4), logical (0));
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60 %!assert (isprime (3), logical (1));
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61 %!assert (isprime (magic (3)), logical ([0, 0, 0; 1, 1, 1; 0, 0, 1]));
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62 %!error isprime ()
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63 %!error isprime (1, 2)