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## Copyright (C) 1996 John W. Eaton
##
## 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, 59 Temple Place - Suite 330, Boston, MA
## 02111-1307, USA.
## usage: list_primes (n)
##
## List the first n primes. If n is unspecified, the first 30 primes
## are listed.
##
## The algorithm used is from page 218 of the TeXbook.
## Author: jwe
function retval = list_primes (n)
if (nargin > 0)
if (! is_scalar (n))
error ("list_primes: argument must be a scalar");
endif
endif
if (nargin == 0)
n = 30;
endif
if (n == 1)
retval = 2;
return;
endif
if (n == 2)
retval = [2; 3];
return;
endif
retval = zeros (1, n);
retval (1) = 2;
retval (2) = 3;
n = n - 2;
i = 3;
p = 5;
while (n > 0)
is_prime = 1;
is_unknown = 1;
d = 3;
while (is_unknown)
a = fix (p / d);
if (a <= d)
is_unknown = 0;
endif
if (a * d == p)
is_prime = 0;
is_unknown = 0;
endif
d = d + 2;
endwhile
if (is_prime)
retval (i++) = p;
n--;
endif
p = p + 2;
endwhile
endfunction
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