Re: Calculate propabilities without recursion? Coin toss.

Your function fac results in n * (n-1) * (n-2) ... * 1. This can be easily calculated using a loop:

my $res = 1;
for(my $i = 2; $i <= $_[0]; $i++) { $res *= $i; }
return $res;
[download]

update: However that is probably not solving your issue with -1.#IND, which indicates that your numbers are getting too big; others propose to add

use bignum;
[download]

to the beginning of your script...

Comment on Re: Calculate propabilities without recursion? Coin toss. Select or Download Code

Replies are listed 'Best First'.
Re^2: Calculate propabilities without recursion? Coin toss. by Microcebus (Beadle) on Mar 16, 2011 at 13:11 UTC
Thanks allot, using bignum works. But makes the whole very very slowly. I want to run this script up to 10000 times with n=up to 5000. This will take weeks... Any suggestions?	[reply]
Re^3: Calculate propabilities without recursion? Coin toss. by happy.barney (Friar) on Mar 16, 2011 at 14:50 UTC
Memoize (Attribute::Memoize) `fac`. Btw: `n!/k! = List::Util::reduce { $a * $b } $k+1 .. $n`	[reply] [d/l] [select]
Re^3: Calculate propabilities without recursion? Coin toss. by ikegami (Patriarch) on Mar 16, 2011 at 14:49 UTC
It wouldn't surprise me if 5000! is larger than the number of atoms in the universe. Would you care to reconsider that?	[reply]
Re^4: Calculate propabilities without recursion? Coin toss. by SuicideJunkie (Vicar) on Mar 16, 2011 at 17:49 UTC
In fact, a measly 65! = 8x10⁹⁰, which is significantly bigger than the number of atoms in the visible universe (10⁷⁸ to 10⁸²).	[reply]
Re^2: Calculate propabilities without recursion? Coin toss. by Anonymous Monk on Mar 17, 2011 at 15:01 UTC
This is the factorial function, which is a special case of the gamma function. If you are going to use this number in ratios, especially in combination with other gamma functions, what you might be better off calculating is the log-gamma function.	[reply]