php variance

function variance ($a)
{
    /** variable and initializations */
    $the_variance = 0.0;
    $the_mean = 0.0;
    $the_array_sum = array_sum($a);
    $number_elements = count($a);                                                                     

    /** calculate the mean */
    $the_mean = $the_array_sum / $number_elements;

    /** calculate the variance */
    for ($i = 0; $i < $number_elements; $i++)
    {
        /** sum the array */
        $the_variance = $the_variance + ($a[$i] - $the_mean) * ($a[$i] - $the_mean);
    }

    $the_variance = $the_variance / ($number_elements - 1.0);

    /** return the variance */
    return $the_variance;
}