good morning! what's the quest today?

2014-7

Can I post my answer right now ;)

If you won't be here in two hours, then sure.

Announcement: Only two months left to enter (or refer people to enter) the annual APL Problem Solving Competition.

I believe it is {⍺÷⍺∨⍵}

Yup, that's one neat way to write it.

The problem formulation is like "Find a minimal positive number N to have 0=(○⍺)|N×○⍵"

having the dyalog tty open in a specific directory, how do I )ed a file in that directory?

I you can open a new terminal to do that

@Razetime Doesn't )ed ./filename.ext work?

@Adám ah the ./ is needed

Otherwise the interpreter cannot know that you're not referring to an APL name.

how do I create a new file with the given name and then )ed it?

Just )ed it, and it should be created.

hm. I just tried it and it does nothing.

I think the interpreter wants to ask, but the TTY provides no UI for that, so it may just answer "no". Try with RIDE.

oh. I guess I'll just ⎕CMD the file creation then.

Or just ⎕NPUT it.

quest in 5 minutes

Probably a short one today.

> Write a dfn which takes the diameters of a stationary and a mobile circle and returns the number of revolutions the mobile must traverse until the tangent points meet again.

tacit version of @LdBeth's solution: ⊣÷∨

LdBeth's answer tacified: ⊣÷∨. With ∧ ≡ ×÷∨ this can be rewritten to ∧÷⊢

Yeah, those two.

Heh, funny that the solution works even when rotated 180°.

yeah lol

Of course, if we didn't have LCM or GCD, we'd have to implement those ourselves.

Or I guess one could simulate it by repeatedly adding until the remainder would be 0.

1{0=⍺|⍺⍺×⍵:⍺⍺ ⋄ ⍺((⍺⍺+1)∇∇)⍵} seems to work.

Does the test system contain cases with very large outputs?

I tried {1+⍣(0=⍺|⍵×⊣)0} but that times out

Probably not. Let's have a look…

@ovs Because ⍣ always applies the function once.

/stolen from l/maths.k
gcd:*|(*:)(|!\)/,
f:{x%gcd[x;y]}

1= \f.10 10
2= \f.10 5
5= \f.5 7

^ solution in ngn/k

@ovs No, never above 20.

@Adám But it works for the small cases, at least in 18.2

Did you try with 0?

No, I see

@PyGamer0 Want to translate that back to APL?

@Adám hmm let me try...

APL2's idiom library has GCD←{⌈/(∧/0=V∘.|⍺ ⍵)/V←⍳⍺⌊⍵}

i cant port the k version..

Oh well, then I guess we're done. Unless someone else wants to have a go.

Go The Distance coming up next week!

@PyGamer0 I think the gcd function is roughly {⊃⌽|\⍤⌽⍣(0=⊃⍤⊣)⍺,⍵}

or full tacit: ⊢/|\⍤⌽⍣(0=⊃⍤⊣)⍤,

Now I understand why 0|X is X, it is very convenient

Yup.

Sorry, missed today's session. My final solution was exactly as mentioned.

@Richard Btw, some people frown at the phrase "final solution".

What does it mean then? I meant to say I had different solutions before I discovered APL had built in GCD.

Oh yeah, it is perfectly clear what you meant, but people think of this.

Ah, ok I only knew the German word. I never translate or use English for German words. Thanks for mentioning.