B 2丌rr+1 S+2 122兀 2 sr r+w S+12 S+卫,+W1 n 2丌 s+w IL In- S+w 2丌 S|1+ +W1 M=1 S+W2 丌 1++y2 0 1 0 12 2 1 0 2 2 1 2 1 0 2 2 2 1 12 2 0 2 2 1 1 1 2 1 1 2 = ln ln 2 = ln 2 1 ln 2 1 S w S B I r r w IL dr r r w S w S w w IL S S w S W IL w S S w S W M L I w S S w             +   = −     +   = −     +   + + +   −   + +     +   + + = =     +   + 