/**
* Computes the population standard deviation for the numbers
* in this list
* @return string
*/
public function stdDev()
{
Number::setScale(static::NUMERIC_FUNCTIONS_SCALE);
$mean = $this->average();
$squares = new static();
foreach ($this->_Arr as $num) {
$squares->add(Number::pow(Number::sub(\strval($num), $mean), '2'));
}
return Number::sqrt($squares->average());
}
protected function setUp()
{
Number::setScale(0);
}
