Math
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<?php
#This function returns the standard deviation of an array
#of numerical values where $std is the array name.
function standard_deviation($std)
{
$total;
while(list($key,$val) = each($std))
{
$total += $val;
}
reset($std);
$mean = $total/count($std);
while(list($key,$val) = each($std))
{
$sum += pow(($val-$mean),2);
}
$var = sqrt($sum/(count($std)-1));
return $var;
}
?>
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Usage Example
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function standard_deviation($std)
{
$total;
while(list($key,$val)=each $std))
{
$total += $val;
}
reset($std);
$mean = $total/count($std);
while(list($key,$val) = each($std))
{
$sum += pow(($val-$mean),2);
}
$var = sqrt($sum/(count($std)-1));
return $var;
}
$values="1,2,2,4,4,4,5,5,6,6,3,3,4,8,7";
$std = explode(",",$values);
print standard_deviation($std);
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