� � ӭ ʹ � � u е � � ƻ � � � � mu �

, � � 2 � � � � � � � � � � � �. � � � � � � � �, ɡ � � � �Ŀ fell

2.4 ƽ � � � ĸ ˻ � � � � Ļ � � � � � � �

һ � � � � � � � � � �

� � � � � � � � � � � �

1. � � � � � Ǻ � ѹ � � � �

2. � � � �

� ˷ � � � � 㣺

� � � � � � � � lambda � � a

Ŀ fell� � һ � �� � һ � &western Σ � � � � �. � � � � � �. � � � � � � � �, ɡ � � � � � � ƣ �