傅里葉變換
http://vdisk.weibo.com/s/aW42jaPITUNHa
http://www.docin.com/p-657665236.html
https://www.zhihu.com/question/22202980/answer/20973635
http://blog.csdn.net/baimafujinji/article/details/10931621
正態分佈
https://cos.name/2013/01/story-of-normal-distribution-1/
複變函數與積分變換
https://wenku.baidu.com/view/3cc3cfc2aef8941ea66e0505.html
協方差矩陣
http://www.cnblogs.com/nsnow/p/4758202.html