public static function mean(array $numbers)
{
if (empty($numbers)) {
return null;
}
return array_sum($numbers) / count($numbers);
}
/** * Sum of squares deviations * * ∑⟮xᵢ - μ⟯² * * @param array $numbers * * @return number */ public static function sumOfSquaresDeviations(array $numbers) { if (empty($numbers)) { return null; } $μ = Average::mean($numbers); $∑⟮xᵢ − μ⟯² = array_sum(array_map(function ($xᵢ) use($μ) { return pow($xᵢ - $μ, 2); }, $numbers)); return $∑⟮xᵢ − μ⟯²; }