public function setLowerBound($lowerBound)
    {
        if (is_float($lowerBound) === true) {
            $this->lowerBound = $lowerBound;
        } else {
            $msg = "The 'lowerBound' argument must be a float value, '" . gettype($lowerBound) . "' given.";
            throw new InvalidArgumentException($msg);
        }
    }