參考

1. Recommender: An Analysis of Collaborative Filtering Techniques
   Chapter 3.4: http://cs229.stanford.edu/proj2014/Christopher%20Aberger,%20Recommender.pdf
2. Collaborative Filtering for Implicit Feedback Datasets
   Chapter 4: https://www.researchgate.net/publication/220765111_Collaborative_Filtering_for_Implicit_Feedback_Datasets

C measures the confidence of the observing p.
C藉由算法去決定，此篇文章用的C和Ｐ是參考第二個reference。
reference 2是原始論文裡面有很詳細的介紹可以參考一下。