Recommender Popularity Bias (2D): The Rich-Get-Richer Feedback Loop

Recommendation systems don't just reflect what users like — the act of recommending changes what gets seen, which changes what gets interacted with, which changes what gets recommended next. This 2D simulator makes that closed loop visible across three linked panels: a radial exposure chart where 72 catalogue items sit as bars around a ring, a live Lorenz curve quantifying inequality, and a rolling history of Gini coefficient and top-10% share. Push the popularity bias α up and watch a handful of bars pull away into a spike while the Lorenz curve sags toward the bottom-right corner; raise the exploration rate ε and watch both flatten back out. Drag the radial chart to rotate your view of the catalogue while the feedback loop runs.