Mercurial > octave-nkf
comparison scripts/miscellaneous/list_primes.m @ 68:46807fe3db5b
[project @ 1993-08-19 02:50:52 by jwe]
Initial revision
| author | jwe |
|---|---|
| date | Thu, 19 Aug 1993 02:50:52 +0000 |
| parents | |
| children | 16a24e76d6e0 |
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| 67:2876864f1fdb | 68:46807fe3db5b |
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| 1 function retval = list_primes (n) | |
| 2 | |
| 3 # usage: list_primes (n) | |
| 4 # | |
| 5 # List the first n primes. If n is unspecified, the first 30 primes | |
| 6 # are listed. | |
| 7 # | |
| 8 # The algorithm used is from page 218 of the TeXbook. | |
| 9 | |
| 10 if (nargin > 0) | |
| 11 if (! is_scalar (n)) | |
| 12 error ("list_primes: argument must be a scalar"); | |
| 13 endif | |
| 14 endif | |
| 15 | |
| 16 if (nargin == 0) | |
| 17 n = 30; | |
| 18 endif | |
| 19 | |
| 20 if (n == 1) | |
| 21 retval = 2; | |
| 22 return; | |
| 23 endif | |
| 24 | |
| 25 if (n == 2) | |
| 26 retval = [2; 3]; | |
| 27 return; | |
| 28 endif | |
| 29 | |
| 30 retval = zeros (1, n); | |
| 31 retval (1) = 2; | |
| 32 retval (2) = 3; | |
| 33 | |
| 34 n = n - 2; | |
| 35 i = 3; | |
| 36 p = 5; | |
| 37 while (n > 0) | |
| 38 | |
| 39 is_prime = 1; | |
| 40 is_unknown = 1; | |
| 41 d = 3; | |
| 42 while (is_unknown) | |
| 43 a = fix (p / d); | |
| 44 if (a <= d) | |
| 45 is_unknown = 0; | |
| 46 endif | |
| 47 if (a * d == p) | |
| 48 is_prime = 0; | |
| 49 is_unknown = 0; | |
| 50 endif | |
| 51 d = d + 2; | |
| 52 endwhile | |
| 53 | |
| 54 if (is_prime) | |
| 55 retval (i++) = p; | |
| 56 n--; | |
| 57 endif | |
| 58 p = p + 2; | |
| 59 | |
| 60 endwhile | |
| 61 | |
| 62 endfunction |