Agreed. I started from this article a few years ago, and was frustrated enough by: > So that means, while I know what it does, I don't really know how, since a

Agreed. I started from this article a few years ago, and was frustrated enough by: > So that means, while I know what it does, I don't really know how, since all the work is in that mysterious function. that I spent the time to work it out myself. (answer: It arises from discretising the Laplacian -- 6 is the number of direct neighbours in 3D)