Mercurial > hg > octave-nkf
diff scripts/specfun/isprime.m @ 5827:1fe78adb91bc
[project @ 2006-05-22 06:25:14 by jwe]
author | jwe |
---|---|
date | Mon, 22 May 2006 06:25:14 +0000 |
parents | |
children | 93c65f2a5668 |
line wrap: on
line diff
new file mode 100644 --- /dev/null +++ b/scripts/specfun/isprime.m @@ -0,0 +1,53 @@ +## Copyright (C) 2000 Paul Kienzle +## +## This file is part of Octave. +## +## Octave is free software; you can redistribute it and/or modify it +## under the terms of the GNU General Public License as published by +## the Free Software Foundation; either version 2, or (at your option) +## any later version. +## +## Octave is distributed in the hope that it will be useful, but +## WITHOUT ANY WARRANTY; without even the implied warranty of +## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU +## General Public License for more details. +## +## You should have received a copy of the GNU General Public License +## along with Octave; see the file COPYING. If not, write to the Free +## Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA +## 02110-1301, USA. + +## -*- texinfo -*- +## @deftypefn {Function File} {} isprime (@var{n}) +## +## Return true if @var{n} is a prime number, false otherwise. +## +## Something like the following is much faster if you need to test a lot +## of small numbers: +## +## @example +## @var{t} = ismember (@var{n}, primes (max (@var{n} (:)))); +## @end example +## +## If max(n) is very large, then you should be using special purpose +## factorization code. +## +## @seealso{primes, factor, gcd, lcm} +## @end deftypefn + +function t = isprime (n) + if (! isscalar (n)) + nel = numel (n); + t = n; + for i = 1:nel + t(i) = isprime (t(i)); + endfor + elseif (n != fix (n) || n < 2) + t = 0; + elseif (n < 9) + t = all (n != [4, 6, 8]); + else + q = n./[2, 3:2:sqrt(n)]; + t = all (q != fix (q)); + endif +endfunction