On Sat, May 21, 2022 at 3:39 AM Adrien Mathieu <adrien.lc.math...@gmail.com> wrote: > It took me some time to understand why you were mentioning A%.A, as > matrix multiplication is not commutative. Turns out, by reading the > documentation, that x%.y is actually (%.y) +/ .* x, not x +/ .* %.y as I > implicitly assumed. Btw, why is that? Why does dividing on the right by > y actually multiplies on the left by the inverse? Isn't that weird?
Hmm... Well, one answer is that that's how it's documented -- https://www.jsoftware.com/help/dictionary/d131.htm But another answer might have to do with how E.E. McDonnell had originally implemented this -- (fourth paragraph of the introduction at https://www.jsoftware.com/papers/eem/sqrt1.htm#... E.E. McDonnell spent a lot of time working on x-ray crystallography techniques, and also had some formative influences on J. See https://dl.acm.org/doi/10.1145/206944.206985 for example. And, the techniques for extracting crystal structure from x rays are... interesting.) But, also, I guess an underlying problem is that +/ .* is not commutative. I hope this helps, -- Raul ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
