programming challenge

this challenge has already been mentioned on slashdot but i thought it was interesting to refer to it here in that one of the more elegant solutions was in J , which given the recent death of Dr. Kenneth Iverson made an example of his nice work (in language design) especially poignant
the challenge;
J solution
the author of the j solution's live journal thread on the challenge.

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Can anyone point to a tutorial on J?

Can anyone provide a tutorial on J for either functional programmers or Java programmers? I can't make head nor tails of the syntax, and I don't know APL, but it looks interesting. I've seen old texts on APL, but the concept of an Array-Oriented Programming Language is foreign to me. Is it that all functions map/fold/iterate?


The site has a lot of information.


That helps.


I think I mentioned this on LtU before, but I tried to build an APL to J Operator Comparison a while back. If anyone has some suggestions for the missing pieces or can point to a more exact comparison, it'd be helpful.

apl to j operator comparisons

not familiar with apl from working experience, but in J

inner product: +/ .*
outer product: */
catenate: the same , as in a,b
ravel: two types ,b string out and ,.b vector to 1 column matrix.
scan: /\

Xavier's non-APL/J challenge

Xavier Noria has a programming challenge at that may be interest here.

POSTSCRIPT: The site seems to be down right now, but it's in the Google cache.


If the model is already described, what is the challenge?

As a side note: if there is no friction, then the only equilibrium points that are possible (except ends of the track) are unstable, and unless appropriate care is taken, simulation around them can get highly unreliable. For example, some tracks may exhibit unterminating behavior. Oh, is this the challenge?

PS: I hope I didn't write a spoiler, did I? The quiz has expired, but I still would refrain from stealing analytical fun :-)

PPS: All in all, the challenge seems to define the task, not to program it. For example, it is not clear (to me) whether the car can fly, or it is bound to the rail (and if it flies, then whether it is limited by the rail above it, or only under it), and whether vertical/horizontal components of the speed can convert to each other at the junctions (seems yes, otherwise energy preservation would not hold), etc.