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annotate scripts/specfun/isprime.m @ 17173:bb60b1bb47cf

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view.m: Fix args undefined error when calling with two arguments
author Max Brister <max@2bass.com>
date Sat, 03 Aug 2013 17:23:44 -0600
parents f3d52523cde1
children
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72c96de7a403 maint: update copyright notices for 2012
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1 ## Copyright (C) 2000-2012 Paul Kienzle
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2 ## Copyright (C) 2010 VZLU Prague
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3 ##
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4 ## This file is part of Octave.
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5 ##
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6 ## Octave is free software; you can redistribute it and/or modify it
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7 ## under the terms of the GNU General Public License as published by
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8 ## the Free Software Foundation; either version 3 of the License, or (at
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9 ## your option) any later version.
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10 ##
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11 ## Octave is distributed in the hope that it will be useful, but
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12 ## WITHOUT ANY WARRANTY; without even the implied warranty of
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13 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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14 ## General Public License for more details.
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15 ##
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16 ## You should have received a copy of the GNU General Public License
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17 ## along with Octave; see the file COPYING. If not, see
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18 ## <http://www.gnu.org/licenses/>.
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19
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20 ## -*- texinfo -*-
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21 ## @deftypefn {Function File} {} isprime (@var{x})
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22 ## Return a logical array which is true where the elements of @var{x} are
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23 ## prime numbers and false where they are not.
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24 ##
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25 ## If the maximum value in @var{x} is very large, then you should be using
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26 ## special purpose factorization code.
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27 ##
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28 ## @example
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29 ## @group
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30 ## isprime (1:6)
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31 ## @result{} [0, 1, 1, 0, 1, 0]
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32 ## @end group
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33 ## @end example
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34 ## @seealso{primes, factor, gcd, lcm}
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35 ## @end deftypefn
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36
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37 function t = isprime (x)
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38
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39 if (nargin == 1)
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40 if (any ((x != floor (x) | x < 0)(:)))
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41 error ("isprime: needs positive integers");
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42 endif
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43 maxn = max (x(:));
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44 ## generate prime table of suitable length.
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45 maxp = min (maxn, max (sqrt (maxn), 1e7)); # FIXME: threshold not optimized.
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46 pr = primes (maxp);
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47 ## quick search for table matches.
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48 t = lookup (pr, x, "b");
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49 ## take the rest.
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50 m = x(x > maxp);
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51 if (! isempty (m))
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52 ## there are still possible primes. filter them out by division.
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53 if (maxn <= intmax ("uint32"))
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54 m = uint32 (m);
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55 elseif (maxn <= intmax ("uint64"))
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56 m = uint64 (m);
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57 else
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58 warning ("isprime: too large integers being tested");
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59 endif
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60 pr = cast (pr(pr <= sqrt (maxn)), class (m));
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61 for p = pr
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62 m = m(rem (m, p) != 0);
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63 if (length (m) < length (pr) / 10)
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64 break;
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65 endif
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66 endfor
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67 pr = pr(pr > p);
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68 mm = arrayfun (@(x) all (rem (x, pr)), m);
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69 m = m(mm);
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70 if (! isempty (m))
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71 m = cast (sort (m), class (x));
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72 t |= lookup (m, x, "b");
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73 endif
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74 endif
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75
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76 else
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77 print_usage ();
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78 endif
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79
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80 endfunction
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81
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82
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83 %!assert (isprime (3), true)
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84 %!assert (isprime (4), false)
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85 %!assert (isprime (magic (3)), logical ([0, 0, 0; 1, 1, 1; 0, 0, 1]))
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86
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87 %!error isprime ()
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88 %!error isprime (1, 2)
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89