Luhn Algorithm in PHP

Here's the Luhn in PHP.  Check it out.

<?php
    function luhnCheckSum($accountNumber)
                   { 
              
                                         
                    $accountArray = array();
                    $total = 0;
                    $i = 0;
                  
                   
                   
                    for($i = 0; $i < strlen($accountNumber) - 1; $i++)
                    {
                      
                      
                        if (!isset($accountArray[$i])) {$accountArray[$i] = 0;}
                      
                        $accountArray[$i] = intval(substr($accountNumber, $i,1));
                      
                       
                      
                        if ( ($accountArray[$i] > 9)  && ($i%2 == 1) )
                        {
                            $accountArray[$i] = 1 + $accountArray[$i] % 10;
                          
                              
                        }
                          
                        $total = $total + $accountArray[$i];
                    }
                  
                    $total *= 9;
                  
                    $lastDigit = 0;
                  
                    $lastDigit = $total % 10;
                  
                    $checkSumDigit = 0;
                  
                    $checkSumDigit = intval(substr($accountNumber, 9, 1));
                  
                    if ($lastDigit === $checkSumDigit)
                    {
                        return true; 
                    }
                    else
                    {
                        return false;
                    }
                  
                }


?>