The ELO Score
Early apps ranked users by "desirability". If a popular person swipes right on you, your score goes up. Modern apps use vectors of taste.
Preferences vs Behavior
Users say they want "Kind, 6ft tall". They swipe on "Hot, Bad Boy". Algorithms trust behavior (swipes) over stated preferences.
Location Geohashing
Use Geohash or S2 cells for efficient "people near me" queries. Calculate radius search on grid cells, not raw coords.
The Stability/Retention Paradox
A perfect match means two users leave the app (churn). Apps must balance successful matches with keeping users swiping.
Cold Start Problem
New users need exposure to get a "score". Boost new profiles temporarily to gather data and hook them with matches.
Safety and Spam
Detect bots early. Verify photos with selfie-challenges (pose matching). Block device IDs of banned predators.
Monetizing Desperation
Super Likes and Boosts work because they bypass the black-box algorithm. Selling "visibility" is the core business model.