MathPHP\Functions\Map\Single::square PHP Метод

    public static function square(array $xs) : array
    {
        return array_map(function ($x) {
            return $x ** 2;
        }, $xs);
    }

 /**
  * Sum of squares
  *
  * ∑⟮xᵢ⟯²
  *
  * @param array $numbers
  *
  * @return number
  */
 public static function sumOfSquares(array $numbers)
 {
     if (empty($numbers)) {
         return null;
     }
     $∑⟮xᵢ⟯² = array_sum(Map\Single::square($numbers));
     return $∑⟮xᵢ⟯²;
 }