概率论与数理统计数学期望与方差专项(
http://wenku.baidu.com/link?url=PrSbKPvpmYMrViIqmlo8XyhvjZcKobeCNip3CWxx3GRv8Rib9rg5U4fcQevftJfBmaUHn7sdaYORvFrRziQqz9T_AGQjbj1_K1H5ymvEtb3
)协方差的意义和计算公式(http://www.cnblogs.com/ywl925/archive/2013/07/24/3210822.html)
如何通俗易懂地解释「协方差」与「相关系数」的概念?(https://www.zhihu.com/question/20852004)
最大似然估计法(http://wenku.baidu.com/link?url=hKuo72uKsPVME5vF0xseSZXSynyYcanjYUFth9G7nDbOZqK5EiC3_bLJfL9155rq5pTrovaXJpIaBl2fMnfFzn53hSuTsrjrT0nd4BJLxHO)