--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main/specfun/isprime.m	Wed Oct 10 19:54:49 2001 +0000
@@ -0,0 +1,45 @@
+## Copyright (C) 2000 Paul Kienzle
+##
+## This program 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 of the License, or
+## (at your option) any later version.
+##
+## This program 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 this program; if not, write to the Free Software
+## Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+
+## usage: isprime(n)
+## Return true if n is a prime number, false otherwise.
+##
+## Something like the following is much faster if you need to test a lot
+## of small numbers:
+##    t = ismember (n, primes (max (n (:))));
+## If max(n) is very large, then you should be using special purpose 
+## factorization code.
+##
+## See also: primes, factor, gcd, lcm
+
+function t = isprime(n)
+  if !is_scalar(n)
+    [nr, nc] = size(n);
+    t = n;
+    for i=1:nr
+      for j=1:nc
+	t(i,j) = isprime(t(i,j));
+      endfor
+    endfor
+  elseif (n != fix(n) || n < 2)
+    t = 0;
+  elseif n < 4
+    t = 1;
+  else
+    q = n./[2:sqrt(n)];
+    t = all (q != fix(q));
+  endif
+endfunction