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1 ## Copyright (C) 2000 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 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, Inc., 51 Franklin Street, Fifth Floor, Boston, MA |
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18 ## 02110-1301, USA. |
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19 |
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20 ## -*- texinfo -*- |
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21 ## @deftypefn {Function File} {} isprime (@var{n}) |
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22 ## |
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23 ## Return true if @var{n} is a prime number, false otherwise. |
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24 ## |
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25 ## Something like the following is much faster if you need to test a lot |
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26 ## of small numbers: |
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27 ## |
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28 ## @example |
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29 ## @var{t} = ismember (@var{n}, primes (max (@var{n} (:)))); |
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30 ## @end example |
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31 ## |
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32 ## If max(n) is very large, then you should be using special purpose |
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33 ## factorization code. |
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34 ## |
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35 ## @seealso{primes, factor, gcd, lcm} |
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36 ## @end deftypefn |
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37 |
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38 function t = isprime (n) |
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39 if (! isscalar (n)) |
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40 nel = numel (n); |
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41 t = n; |
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42 for i = 1:nel |
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43 t(i) = isprime (t(i)); |
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44 endfor |
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45 elseif (n != fix (n) || n < 2) |
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46 t = 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 endfunction |
