"Under the random selection of a tiny subset of less than 0.1 percent of the total population, the density of the social graph of the citizens is massively redu

"Under the random selection of a tiny subset of less than 0.1 percent of the total population, the density of the social graph of the citizens is massively reduced, while the "terrorist" cluster remains strongly interconnected." There is no indication in the slides that the feature calculations are done on the smaller subgraph. The above comment doesn't hold if the calculations are done on the entire graph and then the 100k are sampled for training.