Loving the Spotify recommendation emails I get, although probably not for the reasons they’d prefer. The best thing about them is that they give the reasoning behind the recommendations. Based on this you can get a rough visualization of the Eigenvalue matrix they use to make these suggestions. For example:

Simon & Garfunkel

The most successful folk-rock duo of the 1960s, Paul Simon and Art Garfunkel crafted a series of memorable hit albums and singles featuring their… (Read more)

Because you’ve listened to Buddy Holly, Jimi Hendrix, Johnny Cash and The Jimi Hendrix Experience.

This is probably the most novel suggestion I’ve been given. Not novel in the sense that I’d probably never listened to Simon & Garfunkel, but novel in the way the suggestion came about. None of the vectors (groups/bands/artists) used to make the suggestion are close to the folk-rock genre yet if you average out the vectors, I can see how you’d land squarely along the vector that gives you Simon & Garfunkel.

Another interesting bit of vector math is the one that came up with The Clash as a suggestion. Here we have:

The Clash

The Sex Pistols may have been the first British punk rock band, but the Clash were the definitive British punk rockers. Where the Pistols were… (Read more)

Because you’ve listened to Beastie Boys, Jimi Hendrix, The Jimi Hendrix Experience and The Kinks.

Again, you can see where The Clash are like the pre-rap Beastie Boys with more complex songcraft than most “punk” bands a la Hendrix, with sometimes clever lyricism a la The Kinks. This recommendation also makes sense, even if it is for a group that is not all that far off the beaten path.

Vector analysis and the related mathematics was probably the one subject that completely blew my mind back in grad school. Recommendation engines are truly fascinating things. Not only do they possibly show you some synthetic reasoning, but they also give you some pretty decent insight into the folks who set up the matrix that is being operated on. So even though the recommendations Spotify sends along are pretty middle of the road, they still provide some great entertainment.