svd for recommendation

reference:

《A Guide to Singular Value Decomposition for Collaborative Filtering》

《Collaborative Filtering for Netflix》

#personal rank reference:

http://blog.csdn.net/harryhuang1990/article/details/10048383 用PersonalRank实现基于图的推荐算法

https://github.com/wangrn/RecommendationSystemStudy/blob/master/PersonalRank.py