Math
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<?php
/*
In this code fraction, there r 3 function that run on mean or average and skewness and kurtosis.
Program by : dhiranuntk@hotmail.com
Date : Feb.18,2001
*/
function mean(&$array) {
$average = 0;
while (list($key, $val)=each($array)) $average += $val;
reset($array);
$average /= count($array);
return $average;
}
function skewnessandkurtosis($array, &$skew, &$kurt) {
$skew = "N/A";
$kurt = "N/A";
$amount = count($array);
if ($amount > 2) {
for ($i = 0, $m2 =0,$m3=0,$m4=0; $i < $amount; $i++) {
$array [$i] -= mean($array);
$m2 += pow($array[$i], 2);
$m3 += pow($array[$i], 3);
$m4 += pow($array[$i], 4);
}
$m2 /= $amount;
$m3 /= $amount;
$m4 /= $amount;
$skew = $m3 / pow($m2, 1.5);
$skew *= sqrt($amount*($amount-1))/ ($amount-2);
if ($amount > 3) {
$kurt = ($m4/ pow($m2, 2))-3;
$kurt = (($amount+1)*$kurt)+6;
$kurt *= ($amount-1)/(($amount-2)*($amount-3));
}
}
}
?>
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Usage Example
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<?
$samplearray = array(1.8,1.9,1.2,1.5,1.7);
skewnessandkurtosis($samplearray, $skew, $kurt);
echo "<p>Data average = ". mean($samplearray)."</p>";
echo "<p>skewness = $skew </p>";
echo "<p>kurtosis=$kurt</p>";
?>
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