/**
* Calculates the standard deviation of the specified elements. If the given
* elements is a population then the population standard deviation is
* calculated otherwise the sample standard deviation.
*
* @param array $elements list of element from a sample or population
* distribution.
* @param boolean $population true if the element list is a population
* distribution.
*
* @return the variance of the specified elements.
*/
public static function stdv($elements, $population = FALSE)
{
$stdv = 0.0;
$variance = 0.0;
$n = count($elements);
$mean = Math::mean($elements);
$variance = Math::variance($elements, $population);
$stdv = pow($variance, 0.5);
// $stdv = sqrt($variance);
return $stdv;
}