0 t<1 2(1-t)1<t≤2 w(t=-Cuc(t)= 2(t-3)22<t≤4 () t>4( ) 2 4 2( 3) 2 4 2(1 ) 1 2 0 1 ( ) 2 1 ( ) 2 2 2 C J t t t t t t w t C u t C         −   −    = =