Roger Hui has died(jsoftware.com) |
Roger Hui has died(jsoftware.com) |
Fitting file name, in the spirit of J's terseness.
just found https://crypto.stanford.edu/~blynn/haskell/jfh.html to cross-ref stuff when I get lost
"What is the “best” perm function I can write in APL? This “best” is a benchmark not only on my own understanding but also on advancements in APL over the years." and then shows one he wrote in 1981, one from 1987, then "I worked on perm from time to time in this period [1990-2007] but in J rather than in APL", then one from 2008, and one from 2015, and where future improvements might be found. In a video talk on it he says "some of these sub-expressions can be improved, but the APL language cannot yet express the thought that I have"[2]. I just like that pattern of returning to the same problems and polishing both the language and solution over multiple decades.
[1] https://www.dyalog.com/blog/2015/07/permutations/
[2] https://youtu.be/e0rywC7-i0U?t=2254
[3] talk is taken from his writing here, I think: https://www.jsoftware.com/papers/50/
I hope he gets the recognition he deserves. What he and Iverson have developed is truly unique and powerful.
EDIT: A bit macabre but Ken had his stroke on the 16th of October (2004) and died on the 19th. I know it’s coincidence but my mammalian brain can’t help but ascribe significance.
Knowing geeks, I wouldn't be surprised if part of why he didn't let on was because he didn't want to stop having fun geeking out.
A (likely incomplete) list of his talks can be found here; if you have the time, you should watch at least some of them: https://aplwiki.com/wiki/Roger_Hui
He dedicated a substantial portion of his life to the design and implementation of two of the last truly-unique languages in our field.
We all owe him a degree of debt. If you use numpy, for example, you're actually closer to the heritage of his work than you might imagine; about two steps removed. Start from the top of this thread and work your way down (I am sorry for the source of the link, but none of the frontends cover threads this long and with this many authors):
What is the other one?
He seemed like a mellow, straightforward person and I enjoyed how he explained a one-page long set of c-macros that expanded into the initial J compiler (written by Ken Iverson or someone else).
I remember asking him, "How do you debug something like that" and he said "don't make mistakes".
Some people might enjoy this thread on "A look at the J language: the fine line between genius and insanity (2012)" https://news.ycombinator.com/item?id=16393873
Also this answer here at math stack exchange https://math.stackexchange.com/questions/856153/the-j-progra...
Its very short description of the two-arguments version make it sound like a fold, but that wouldn’t generalise to what looks like a cartesian product, would it?
So the right side of the tilde evaluates to a range 1..10. I think the tilde then turns its left and right into "*/"(1..10, 1..10), resulting in 1..10 * 1..10
Real loss.
Thoughts are with all those who miss him.
The less important one: his Erdős number is 2, thanks to his coauthoring "A generalization of the fast LUP matrix decomposition algorithm and applications" with Shlomo Moran whose Erdős number is 1. (It's not shown on his Wikipedia page, but he's listed at https://en.wikipedia.org/wiki/List_of_people_by_Erd%C5%91s_n... .)
Roger was a great example of "precision with humanity", like Ken Iverson. This was obvious in many ways, and here's an unusual one: I've managed various technical groups over the decades, and Roger was the only person who, when he said he'd have something done by a particular date, was finished by that date, every single time. When he ran into a snag I would sometimes tell him that it would be okay if it took longer, but no, as far as he was concerned he'd made a commitment and was going to meet it, even if that meant working a lot of extra hours.
Rohan Jayasekera
RIP.
My Dad is dying now from it. 83 but the time has gone so fast. He was otherwise in top shape.
I have high hopes for the new blood test that can detect several types of cancer at a very early stage. It's in trials now in the UK.
Is this the reason for the black stripe on HN? Is there a way to click the stripe or otherwise see the reason for it, other than scanning posts for the sad news?
To honor Roger's passing.
A time to reflect.
'f/ x' is 'insert' - i.e. reduce, so that '+/ 1+i.10' yields 55.
'x f/ y' is 'table', inserting 'f' between each pair to form a generalised multiplication table.
The documentation for j is unsurprisingly terse, but it is complete and very helpful.
That is the part which doesn’t make sense to me: `/ v` is `foldl1 () v`, how does that generalise to a cartesian product when applied to >1 sequences?
As a result, the original mathexchange answer introducing / by explaining its unary behaviour (despite that being used nowhere in the answer) is solely a source of confusion.
The distinguishing between arities is a consistent feature of all of these languages. I find fluency comes quickly to it.
Edit: as for intuition between the two, this is sometimes not obvious, but I think it's a sensible generalisation from the monadic case to the dyadic. How else would you want to extend a fold to two arguments?
I don't know that there is one that's useful, but a cartesian product seems like the opposite: a fold is a dimensional reduction (from 1 to 0 at the most basic), a cartesian product is dimensionally preserving (you start with 1 and 1, you end up with 2).
A cartesian product (with a mapping function) might be interpreted as the extension of a map, I don't rightly see how it can be interpreted as the extension of a fold, except in the sense that you can implement essentially any iterative process using folds, but that leads to you every n-dimensional transformation being a possible extension of a fold.
So my answer would mostly be "you would not". You could also define an n-dimensional fold as a fold against a caller-specified dimension, but I don't know how useful that would be (though I guess this sort of folds is used when integrating over time in e.g. reactive interfaces).