Factorial

<?php
    /*
    PHP Mathematics Library - Factorial
    
    Copyright (c) 2008, reusablecode.blogspot.com; some rights reserved.
    
    This work is licensed under the Creative Commons Attribution License. To view
    a copy of this license, visit http://creativecommons.org/licenses/by/3.0/ or
    send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California
    94305, USA.
    */
 
    // Determine the factorial for a given number
    function factorial($x)
    {
        $result = 1;
 
        if ($x > 1)
        {
            for ($i = 2; $i <= $x; $i++)
            {
                $result *= $i;
            }
        }
 
        return $result;
    }
 
    // Returns the number of combinations, without regard to order, of y items that can be made from a pool of x items.
    // Requires factorial()
    function combinatorial($x, $y)
    {
        return (($x >= $y) && ($y > 0)) ? factorial($x) / factorial($y) / factorial($x - $y) : 0;
    }
 
    // Returns the number of permutations, with regard to order, of y items that can be made from a pool of x items.
    // Requires factorial()
    function permutations($x, $y)
    {
        return factorial($x) / factorial($x - $y);
    }
?>