The APL Orchard

3:41 AM

@Bubbler Oh, where? Congrats!

4:18 AM

@Razetime Dyalog 2020 APL Problem Solving Competition

4 hours later…

gvaf

8:15 AM

@Adám yeah started playing with it...

@Bubbler You truly deserved it. I also really appreciate all your APL Wiki contributions.

@gvaf Cool. Let me know if I can be of any help. Where are you holding?

9:03 AM

So I'm trying to find the value that maximized sin ⍵ in ⍳⍵

but something isn't right here {⍳⍵[(⊃⍒)1○⍳⍵]}

never mind, got it

@Razetime While you've probably found that you need to parenthesise the left ⍳⍵, you don't need parentheses around ⊃⍒. However, consider naming ⍳⍵ to avoid computing it twice: {i[⊃⍒1○i←⍳⍵]}

If you're golfing, you can use a train: ⍳⊃⍨∘⊃∘⍒1○⍳

I tried using that train but it doesn't seem to give the right output

tio.run/##SyzI0U2pTMzJT9dNrShJzUtJTfn/…

I'm not sure how to use anonymous functions in the desktop application

9:20 AM

@Razetime Just do f←{i[⊃⍒1○i←⍳⍵]}

Or {i[⊃⍒1○i←⍳⍵]} 10 for immediate execution should work too.

For the train, did you write something like ⍳⊃⍨∘⊃∘⍒1○⍳ 10?

yes

Trains should be parenthesized (⍳⊃⍨∘⊃∘⍒1○⍳) or assigned to a function first f←⍳⊃⍨∘⊃∘⍒1○⍳ before using it.

This works for code golf submission too.

yep but for some reason it's not giving the right output

Here

that's what is supposed to come up I think

I don't get it. What is the exact task?

Q: Integers in cosine

Integers in cosine From trigonometry we know that \$\sin(a) =-\cos(a + \frac{(4*m + 1)\pi}{2})\$ where \$a\$ is an angle and \$m\in\mathbb{Z}\$ (integer). The task For an input of a positive integer \$n\$ calculate the value of the integer \$k\$ with \$n\$ digits that minimizes the difference bet...

and this is my answer so far codegolf.stackexchange.com/a/209831/80214

9:30 AM

Then what doesn't work in the train, except for missing 10*?

I'm not sure

the only thing I was saying is that it wasn't fulfilling the testcases

Not very familiar with trains yet

This gives the values right, so the only step needed is to 10* on the argument.

It can be done with (⍳⊃⍨∘⊃∘⍒1○⍳)10∘*.

But it has the same bytecount with simply using your dfn with an intermediate assignment, so train isn't needed here.

Ah I didn't add the 10* that was why the previous links didn't work

what does ∘ do in these trains?

○

9:48 AM

The ones in ⊃⍨∘⊃∘⍒ are "Beside", where x f∘g y → x f (g y) and f∘g y → f (g y).

So x ⊃⍨∘⊃∘⍒ y → x ⊃⍨ ⊃ ⍒ y → (⊃⍒y)⊃x.

The one in 10∘* is "Bind", which binds one side of a dyadic function to make it a monad.

x∘f y → x f y, (f∘x) y → y f x

ngn

10:15 AM

@Bubbler why do you need i[ ] / ⍳⊃⍨∘ at all? (and congratulations!)

@ngn How I missed that...

11:21 AM

@ngn D'oh!

@Razetime As per ngn, ⊃∘⍒1○∘⍳10∘* or {⊃⍒1○⍳10*⍵} is enough. ⊃∘⍒ or ⊃⍒ gives an index, and using that to select and index (from ⍳) is of course a no-op. Since we only need the argument once, a full program that prompts for input: ⊃⍒1○⍳10*⎕ (The "quad", ⎕, is stdin.) Try it online!

11:47 AM

no-op?

@Razetime NO-effect-OPeration.

NOP (code)

In computer science, a NOP, no-op, or NOOP (pronounced "no op"; short for no operation) is an assembly language instruction, programming language statement, or computer protocol command that does nothing. == Machine language instructions == Some computer instruction sets include an instruction whose explicit purpose is to not change the state of any of the programmer-accessible registers, status flags, or memory. It often takes a well-defined number of clock cycles to execute. In other instruction sets, a NOP can be simulated by executing an instruction having operands that cause the same effect...

cool.

3 hours later…

2:59 PM

Announcement: "Advanced Use of The Rank Operator" webinar in one minute at dyalog.tv

4 hours later…

6:40 PM

is there a way to remove the { ... ⍵ } from this APL expression:
rf ← ((⌈\⌊{⌽⌈\⌽⍵})+.-⊢)

@code_report (⌽⌈\∘⌽)

@dzaima Thanks! ... and interesting. I think I tried (⌽∘⌈\∘⌽) at one point. Are you able to explain why you only need the first ∘

@code_report it creates an atop of 2 functions - (⌽ (⌈\∘⌽)); a jot and an atop is common for 3 sequential monadic functions (you could also usually have 2 jots at the expense of a byte, but \ makes that not work as (⌽∘⌈\∘⌽) is ((⌽∘⌈)\∘⌽))

also, with under, {⌽⌈\⌽⍵} could also be ⌈\⍢⌽

@dzaima i see, so due to binding precedence, i would need to do (⌽∘(⌈\∘⌽)) in order to use jot twice. but that is more verbose than an atop

its odd because the atop train and jot basically serve the same purpose if I understand correctly

composition of two functions

@code_report besides syntax, the tacit atop is equal to ∘ monadically, but dyadically it acts as ⍤

6:54 PM

interesting

and I have no idea what "under" / ⍢ is

doesnt seem to show up in tryapl.org

(and ∘ is equal to ⍤ monadically, so ((f) (g)) is always the same as (f)⍤(g))

@code_report it's not in Dyalog currently. in this case, f⍢g X is (g⍣¯1) f g X - it's implemented in dzaima/APL and Dyalog APL Extended

cool! thanks for your help @dzaima!

4 hours later…

RGS

10:54 PM

@Bubbler nice! Congratulations!

There's still some time left before it happens, but I think you'll enjoy Portugal :P