Mercurial > octave-nkf
annotate scripts/miscellaneous/list_primes.m @ 8874:bd1b1fe9c6e9 ss-3-1-53
bump version info for snapshot
| author | John W. Eaton <jwe@octave.org> |
|---|---|
| date | Wed, 25 Feb 2009 18:35:47 -0500 |
| parents | 81d6ab3ac93c |
| children | eb63fbe60fab |
| rev | line source |
|---|---|
| 7017 | 1 ## Copyright (C) 1993, 1995, 1996, 1997, 2000, 2002, 2005, 2007 |
| 2 ## John W. Eaton | |
| 2313 | 3 ## |
| 4 ## This file is part of Octave. | |
| 5 ## | |
| 6 ## Octave is free software; you can redistribute it and/or modify it | |
| 7 ## under the terms of the GNU General Public License as published by | |
| 7016 | 8 ## the Free Software Foundation; either version 3 of the License, or (at |
| 9 ## your option) any later version. | |
| 2313 | 10 ## |
| 11 ## Octave is distributed in the hope that it will be useful, but | |
| 12 ## WITHOUT ANY WARRANTY; without even the implied warranty of | |
| 13 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
| 14 ## General Public License for more details. | |
| 15 ## | |
| 16 ## You should have received a copy of the GNU General Public License | |
| 7016 | 17 ## along with Octave; see the file COPYING. If not, see |
| 18 ## <http://www.gnu.org/licenses/>. | |
| 245 | 19 |
| 3449 | 20 ## -*- texinfo -*- |
| 21 ## @deftypefn {Function File} {} list_primes (@var{n}) | |
| 22 ## List the first @var{n} primes. If @var{n} is unspecified, the first | |
| 23 ## 30 primes are listed. | |
| 2311 | 24 ## |
| 3449 | 25 ## The algorithm used is from page 218 of the |
| 26 ## @iftex | |
| 27 ## @tex | |
| 6248 | 28 ## {\TeX}book. |
| 3449 | 29 ## @end tex |
| 30 ## @end iftex | |
|
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31 ## @ifnottex |
| 3449 | 32 ## TeXbook. |
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33 ## @end ifnottex |
| 3449 | 34 ## @end deftypefn |
| 68 | 35 |
| 2314 | 36 ## Author: jwe |
| 37 | |
| 2311 | 38 function retval = list_primes (n) |
| 68 | 39 |
| 40 if (nargin > 0) | |
| 4030 | 41 if (! isscalar (n)) |
| 68 | 42 error ("list_primes: argument must be a scalar"); |
| 43 endif | |
| 44 endif | |
| 45 | |
| 46 if (nargin == 0) | |
| 47 n = 30; | |
| 48 endif | |
| 49 | |
| 50 if (n == 1) | |
| 51 retval = 2; | |
| 52 return; | |
| 53 endif | |
| 54 | |
| 55 if (n == 2) | |
| 56 retval = [2; 3]; | |
| 57 return; | |
| 58 endif | |
| 59 | |
| 60 retval = zeros (1, n); | |
| 61 retval (1) = 2; | |
| 62 retval (2) = 3; | |
| 63 | |
| 64 n = n - 2; | |
| 65 i = 3; | |
| 66 p = 5; | |
| 67 while (n > 0) | |
| 68 | |
| 69 is_prime = 1; | |
| 70 is_unknown = 1; | |
| 71 d = 3; | |
| 72 while (is_unknown) | |
| 73 a = fix (p / d); | |
| 74 if (a <= d) | |
| 75 is_unknown = 0; | |
| 76 endif | |
| 77 if (a * d == p) | |
| 78 is_prime = 0; | |
| 79 is_unknown = 0; | |
| 80 endif | |
| 81 d = d + 2; | |
| 82 endwhile | |
| 83 | |
| 84 if (is_prime) | |
| 85 retval (i++) = p; | |
| 86 n--; | |
| 87 endif | |
| 88 p = p + 2; | |
| 89 | |
| 90 endwhile | |
| 91 | |
| 2326 | 92 endfunction |