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comparison scripts/specfun/isprime.m @ 9984:d1cc2e0ddf55

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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
comparison
equal deleted inserted replaced
9983:2d347a2f4a0a 9984:d1cc2e0ddf55
1 ## Copyright (C) 2000, 2006, 2007 Paul Kienzle 1 ## Copyright (C) 2000, 2006, 2007, 2009 Paul Kienzle
2 ## 2 ##
3 ## This file is part of Octave. 3 ## This file is part of Octave.
4 ## 4 ##
5 ## Octave is free software; you can redistribute it and/or modify it 5 ## Octave is free software; you can redistribute it and/or modify it
6 ## under the terms of the GNU General Public License as published by 6 ## under the terms of the GNU General Public License as published by
16 ## along with Octave; see the file COPYING. If not, see 16 ## along with Octave; see the file COPYING. If not, see
17 ## <http://www.gnu.org/licenses/>. 17 ## <http://www.gnu.org/licenses/>.
18 18
19 ## -*- texinfo -*- 19 ## -*- texinfo -*-
20 ## @deftypefn {Function File} {} isprime (@var{n}) 20 ## @deftypefn {Function File} {} isprime (@var{n})
21 ##
22 ## Return true if @var{n} is a prime number, false otherwise. 21 ## Return true if @var{n} is a prime number, false otherwise.
23 ## 22 ##
24 ## Something like the following is much faster if you need to test a lot 23 ## Something like the following is much faster if you need to test a lot
25 ## of small numbers: 24 ## of small numbers:
26 ## 25 ##
27 ## @example 26 ## @example
28 ## @var{t} = ismember (@var{n}, primes (max (@var{n} (:)))); 27 ## @var{t} = ismember (@var{n}, primes (max (@var{n} (:))));
29 ## @end example 28 ## @end example
30 ## 29 ##
31 ## If max(n) is very large, then you should be using special purpose 30 ## If max(n) is very large, then you should be using special purpose
32 ## factorization code. 31 ## factorization code.
33 ## 32 ##
34 ## @seealso{primes, factor, gcd, lcm} 33 ## @seealso{primes, factor, gcd, lcm}
35 ## @end deftypefn 34 ## @end deftypefn
36 35
37 function t = isprime (n) 36 function t = isprime (n)
38 37
39 if (nargin < 1) 38 if (nargin == 1)
39 if (! isscalar (n))
40 nel = numel (n);
41 t = zeros (size (n), "logical");
42 for i = 1:nel
43 t(i) = isprime (n(i));
44 endfor
45 elseif (n != fix (n) || n < 2)
46 t = logical (0);
47 elseif (n < 9)
48 t = all (n != [4, 6, 8]);
49 else
50 q = n./[2, 3:2:sqrt(n)];
51 t = all (q != fix (q));
52 endif
53 else
40 print_usage (); 54 print_usage ();
41 endif 55 endif
42 56
43 if (! isscalar (n))
44 nel = numel (n);
45 t = n;
46 for i = 1:nel
47 t(i) = isprime (t(i));
48 endfor
49 elseif (n != fix (n) || n < 2)
50 t = 0;
51 elseif (n < 9)
52 t = all (n != [4, 6, 8]);
53 else
54 q = n./[2, 3:2:sqrt(n)];
55 t = all (q != fix (q));
56 endif
57 endfunction 57 endfunction
58
59 %!assert (isprime (4), logical (0));
60 %!assert (isprime (3), logical (1));
61 %!assert (isprime (magic (3)), logical ([0, 0, 0; 1, 1, 1; 0, 0, 1]));
62 %!error isprime ()
63 %!error isprime (1, 2)