How Can I Make This Function Return The Kurtosis, It Just Outputs 'Inf' As Of Now.

<?php
    require_once 'variance.php';
    require_once 'mean.php';

    function kurtosis($valArray, $isSample, $isExcess){
     $mean = mean($valArray);
        $variance = 0;
        $mult = 0;
        $moment4 = 0;
        $length = 0;

        foreach($valArray as $k => $moment4):
            $mult -= $mean;
            $mult *= $mult;
            $mult *= $mult;
            $moment4 += $mult;
            $length++;
        endforeach;
        $variance = variance($valArray, $mean, $isSample);
        $moment2 = ($variance *= $variance);
        $kurt = $length *($moment4 / $moment2);
        //normal kurtosis
        if((!$isSample) && (!$isExcess)):
            $kurtosis = $kurt;
            //excess kurtosis
        elseif(($isExcess) && (!$isSample)):
            $kurtosis = ($kurt - 3);
            // sample kurtosis
        elseif((!$isExcess) && ($isSample)):
            $n3 = ($length * $length * $length);
            $n2 = ($length * $length);
            $kurt = $n2 / $n3;
            $kurtosis = $kurt *($moment4 / $moment2);
            //sample excess kurtosis
        else:
            $n3 = ($length * $length * $length);
            $n2 = ($length * $length);
            $kurt = ( ($n2 / $n3) * ($moment4 / $moment2) );
            $kurtosis = $kurt - 3;
        endif;
        return $kurtosis;
    }
?>