Should that be "pairwise maximum" rather than "pairwise sum"?
On 10 Jan 2015 14:55, "Raul Miller" <[email protected]> wrote:
> I guess I can do a low-level view of how the code works. Though I'm
> not going to use sample data from euler 67 - have to leave you
> something to do... instead, I'll use
>
> i.3 3
> 0 1 2
> 3 4 5
> 6 7 8
>
> as the sample data.
>
> So that's this:
> {. (+ 0: ,~ 2: >./\ ])/ i.3 3
> 12
>
> We also don't need : after the numbers, for this particular case, in
> modern versions of J, nor do we need the spaces, and I'm going to want
> this to be compact, in a moment, so:
> {. (+0,~2>./\])/ i.3 3
> 12
>
> Let's start breaking that down. First, let's remove the 'first' verb,
> so we see what it is acting on:
>
> (+0,~2>./\])/ i.3 3
> 12 13 2
>
> Now how did that happen? Well, in this case the / operator inserts its
> verb between the items of its noun. So, that is:
> 0 1 2 (+0,~2>./\]) 3 4 5 (+0,~2>./\]) 6 7 8
> 12 13 2
>
> Next, let's look at just one of these cases to see how it works:
>
> 3 4 5 (+0,~2>./\]) 6 7 8
> 10 12 5
>
> So how does that work? Well, if we count the verbs in (+0,~2>./\])
> there's an even number of them, so the top level structure is a hook.
> And, it's a dyadic hook (with an argument on its left), so that means
> we can just remove the parenthesis in that sentence (need to read the
> documentation on hooks, really - I'm oversimplifying the definitions
> for only their relevance in this case):
>
> 3 4 5 +0,~2>./\] 6 7 8
> 10 12 5
>
> In other words, it's 3 4 5 + the result of the rest of that stuff.
>
> So:
> 0,~2>./\] 6 7 8
> 7 8 0
>
> That's the pair-wise sum of the elements of the list, with a zero
> tacked onto the right hand side.
>
> Again, I'm oversimplifying things here - you should be able to perform
> your own experiments and/or read the definitions either in the
> official dictionary
> http://www.jsoftware.com/help/dictionary/vocabul.htm or in the
> unofficial nuvoc http://www.jsoftware.com/jwiki/NuVoc -- but be sure
> to try things out, some, to help resolve ambiguities and especially
> when you think you understand things (because sometimes things are
> surprising).
>
> So anyways, {. (+ 0: ,~ 2: >./\ ])/ m is, basically:
>
> The first thing from:
>
> adding each row to
> the pairwise sum of
> this result for the previous row
>
> (padding pairwise sums on the right, to keep things the same length)
>
> I hope this helps.
>
> Thanks,
>
> --
> Raul
>
> On Sat, Jan 10, 2015 at 1:06 PM, Roger Hui <[email protected]>
> wrote:
> > Hmm, I bet you a Java solution would be longer, eh? :-)
> >
> > It's been years since I solve Project Euler 67, and I am busy with other
> > things on the weekend, so there'll be a delay in a detailed description.
> > Probably others will chime in meanwhile.
> >
> >
> >
> > On Sat, Jan 10, 2015 at 9:58 AM, oventarb oventarb <[email protected]>
> > wrote:
> >
> >>
> >> Dear Roger Hui!
> >> I solved problem 67 using Java.
> >> What does this code mean:
> >>
> >> {. (+ 0: ,~ 2: >./\ ])/ m
> >> ----------------------------------------------------------------------
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> >>
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