B-S方程 偏微分方程 ac 1 2c2 OC at +-2S +1—三C aS aS 边界条件 7- max Sr-K,Oj3 B－S方程 max{ ,0} 2 1 2 2 2 2 C S K rc S c rS S c S t c T = T − =   +   +   边界条件 偏微分方程 