Merge branch 'master' of https://github.com/ddbourgin/numpy-ml

Author: ddbourgin

trees/README.md

@@ -1,13 +1,12 @@
 # Tree-Based Models
 This module implements:
 
-1. [Decision trees](https://en.wikipedia.org/wiki/Decision_tree_learning) for classification and regression via the CART algorithm
-   (Breiman, Friedman, Olshen, & Stone, 1984).
+1. [Decision trees](https://en.wikipedia.org/wiki/Decision_tree_learning) for classification and regression via the CART algorithm ([Breiman, Friedman, Olshen, & Stone, 1984](https://www.amazon.com/Classification-Regression-Wadsworth-Statistics-Probability/dp/0412048418)).
 2. [Random forests](https://en.wikipedia.org/wiki/Random_forest) for classification and regression (an example of bootstrap
-   aggregating) (Breiman, 2001).
+   aggregating) ([Breiman, 2001](https://www.stat.berkeley.edu/~breiman/randomforest2001.pdf)).
 3. [Gradient-boosted decision
    trees](https://en.wikipedia.org/wiki/Gradient_boosting) for classification and regression (an
-   example of gradient boosted machines) (Friedman, 1999).
+   example of gradient boosted machines) ([Friedman, 1999/2001](https://projecteuclid.org/download/pdf_1/euclid.aos/1013203451)).
 
 ## Plots
 <p align="center">