yahoop gbdt實現
http://lccc.eecs.berkeley.edu/Slides/YeChChZh10_slides.pdf
Ranking with Boosted Decision Trees
http://www.ccs.neu.edu/home/vip/teach/MLcourse/lectures/Schamoni_boosteddecisiontrees.pdf
https://engineering.purdue.edu/kak/Tutorials/Tutorials.html