http://basic.shsmu.edu.cn/jpkc/jianyan/jxjiaoyu/wsw/7.ppt
以及
http://www.google.cn/search?complete=1&hl=zh-CN&newwindow=1&rlz=1T4GGLR_enCN272CN273&q=%E5%8D%8A%E5%90%88%E6%88%90%E9%9D%92%E9%9C%89%E7%B4%A0%E6%9E%84%E6%95%88%E5%85%B3%E7%B3%BB&btnG=Google+%E6%90%9C%E7%B4%A2&meta=&aq=f
都有详细解释,自己找吧!