Since the 1.13 release is out, I have uploaded some new Jupiter notebooks to https://github.com/apache/madlib-site/tree/asf-site/community-artifacts that showcase new features, or reflect user documentation improvements made in http://madlib.apache.org/docs/latest/
These can help you get started. The new notebooks are: Summary-v1.ipynb mlp-v2.ipynb Logistic-regression-v1.ipynb Linear-regression-v1.ipynb kNN-v2.ipynb HITS-v1.ipynb Elastic-net-v2.ipynb Frank