Another quasimetric! Actually a pseudo-quasi-metric. Facebook’s news feed decides what status updates to show you based on three factors:

1. affinity u — how much you like somebody (FB’s guess)
2. type of post w — videos and photos are more interesting than “Chris liked Lili’s status update”
3. 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:

1. never below zero
2. the only “distance of zero” is the distance of something to itself
3. 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.