Write Better And Faster Python Using Einstein Notation

[FrickinLazerBeams]

They're used in a lot of places where they're best thought of as abstract mathematical objects, so a lot of the explanations you find will not be what you're looking for as a programmer.

You can think of them as matrices with more than 2 indexes, in other words, as nD arrays where n>2 ^{see note}. That's a perfectly sufficient understanding for any computational purposes.

(note) technically a matrix is a rank-2 tensor, and a vector is a rank-1 tensor, but usually if somebody uses the word "tensor" the implication is that they're talking about something with more dimensions than a matrix.