When reading papers about math to translate into code, avoid flipping the fuck out about how difficult X will be to implement until you have verified whether the paper's approach actually uses X.

"However, in place of the expensive Fisher kernel¹, we present a new sequence-similarity kernel, the spectrum kernel..."

¹Which happens to be chock full of partial derivatives and other things that are no fun to implement in things that aren't Matlab.

Phew.