高斯判别模型（GDA）原理与推导

https://www.youtube.com/watch?v=nt63k3bfXS0&t=12s

推导:

ccombier/stanford-CS229

https://s3-us-west-2.amazonaws.com/secure.notion-static.com/9c9fb250-7550-4461-99de-9f40b6cdbae1/EM_for_GDA.pdf