On Fri, Dec 10, 2010 at 6:54 AM, Alex Gian <[email protected]> wrote: > Also if you have got SICM, and want a brief intro into their model look > at Chapter 8 (our notation) so that you don't have to glean the > computational approach from reading the book. > http://mitpress.mit.edu/sicm/book-Z-H-79.html#%_chap_8
It is interesting to contemplate the assumptions behind the notation there. Some of them seem to me to be even deeper than the distinction between 'D.' and 'd.' in J. For example, the natural expression in J of the "symbolic value" bit would be something like this: ". bind 'a' This converts a name into a function which always returns the noun assigned to that name as its result. (It's a constant function.) And, where in scheme, you would have a dynamic scope with the value of a name depending on the scope where it is used, J's concept analogous to dynamic scope would be locales -- and the locale used is the one containing the expression at the time it is named (or evaluated). (And you can disassociate an expression from a locale by fixing it or by serializing/deserializing it, for example.) > Finally, what I think will be an interesting J challenge (when I get > round to it) is the implementation of their tuples. The text uses two > types "up" and "down" tuples, with up tuples equivalent to regular > vectors, while down tuples correspond to duals. I am not really sure what that all means -- duality has a lot of meanings, especially in math. But it looks like they are going with something like Einstein's notation (with implicit inner products). Personally, I rather like having explicit inner products, so I will leave treatment of that issue to other people. -- Raul ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
