The discussion is moot. The speed-up factor is a maximum of 2, and you'd have to strain to achieve it:
The logic in inner product is +/@(*"1 _) . This has nice cache effects regarding both read and write. Which is why the release note http://www.jsoftware.com/books/help/release/pdt504.htm said that the speed-up is larger on CPUs with larger on-die cache (i.e. larger on newer CPUs). Moreover, +/@(*"1 _) allows you to exploit 0s in the left argument. +/@(*"1 _) can not be used in the obvious exploitations of symmetry. So you'd probably lose both of the above benefits. So the speed-up factor, already meagre even at 2, is probably something less than 2. ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
