public function get_years($minyear = null, $maxyear = null) {
        if (is_null($minyear)) {
            $minyear = $this->get_min_year();
        }

        if (is_null($maxyear)) {
            $maxyear = $this->get_max_year();
        }

        $years = array();
        for ($i = $minyear; $i <= $maxyear; $i++) {
            $years[$i] = $i;
        }

        return $years;
    }