Excellent intuitive explanations of PCA and some other ML topics

PCA and eigenvector:

• https://skymind.ai/wiki/eigenvector
• https://stats.stackexchange.com/questions/2691/making-sense-of-principal-component-analysis-eigenvectors-eigenvalues

Generative ML algorithms (vs. Discriminative):

• http://cs229.stanford.edu/notes/cs229-notes2.pdf 

Naive Bayes:

• https://www.r-bloggers.com/understanding-naive-bayes-classifier-using-r/