public static function Ir(array &$r) {
    $r[0][0] = 1.0;
    $r[0][1] = 0.0;
    $r[0][2] = 0.0;
    $r[1][0] = 0.0;
    $r[1][1] = 1.0;
    $r[1][2] = 0.0;
    $r[2][0] = 0.0;
    $r[2][1] = 0.0;
    $r[2][2] = 1.0;

    return;
  }