>OK, I'm trying to do some work with matrices that involves transformations >based on local properties of a matrix (neighbouring elements).
As Henry Rich pointed out: the real solution will go via ;.3 tessalations. Have a look at those. Without those ;.3 cuts, the classic approach is this: A little to the left Right down the middle A little to the right, X marks the spot [Godley & Creme, This Sporting Life, 1978] Solve the torus first: use |. to wiggle m up & down (and center), use |."1 to wiggle those matrices left & right (and center) ending up with 9 matrices, the original one and eight shifted ones, where the neighbours get shifted to "the original" position. +/+/, and subtract the original matrix agin if you want to sum up neighbours only, and you are done. You'll need to use "l r a lot to make this work, left as an healthy exercise for you. For the non-torus problem: Pad m with borders of zeroes (easy with , and ,.), do the torus sums, throw away the borders of the sums. Martin ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm