The Boosting Approach to Machine Learning [PDF]: https://www.cs.princeton.edu/courses/archive/spring07/cos424/papers/boosting-survey.pdf
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Gradient Boosting explained [demonstration]:
https://arogozhnikov.github.io/2016/06/24/gradient_boosting_explained.html
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Gradient Boosting Interactive Playground:
https://arogozhnikov.github.io/2016/07/05/gradient_boosting_playground.html