Another quasimetric! Actually a pseudo-quasi-metric. Facebook’s news feed decides what status updates to show you based on three factors:
- affinity u — how much you like somebody (FB’s guess)
- type of post w — videos and photos are more interesting than “Chris liked Lili’s status update”
- time since post d — show newer stuff
The affinity score is a pseudoquasimetric — it’s a one-way measure. If I’m always looking at your profile because you’re a fascinating girl that I met at a party and have been stalking ever since, your updates will show up more in my feed.
But, say you’re the girl and you didn’t think I was interesting at all and never looked at my profile after you Accepted my offer of internet-ual befriendship, my stories won’t be interesting to you and are unlikely to be displayed.
In other words, stalkers don’t show up in your news feed.
The properties of a quasimetric, again, are:
- never below zero ✓
- the only “distance of zero” is the distance of something to itself ✗
- dist( ①→③ ) ≤ dist( ①→② ) + dist( ②→③ ) ✓
Had to drop the second one because there might be lots of FB friends Ⓑ,Ⓒ,Ⓓ,Ⓔ who are not important to me Ⓐ and thus dist( Ⓐ→Ⓑ ) = 0 | Ⓐ≠Ⓑ. (But maybe not?)
Anyway, I threw a "pseudo" on the "quasimetric" just in case lots of different people are of zero interest.
Math news out.