The APL Orchard

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Sherlock9

07:01

I posted this answer to the is_gaussian_prime(z) challenge a bit ago, and I was wondering if there was any golfing that could still be done?

Changing to Extended won't help as the challenge doesn't allow prime factorization builtins and the like

Wait a minute, the answer's not even correct ⍨ One moment

5 hours later…

ngn

11:58

@Sherlock9 4| -> 4||

Sherlock9

12:08

Thanks!

1 hour later…

Sherlock9

13:36

@Adám Do you happen to know
a) How, on Mac RIDE, to change the point at which a line of code wraps from 80 characters?
b) Why `]box -trains=tree` isn't working?
Hope you're having a good Shabbat

ngn

14:31

@Sherlock9 a guard is better than ⍣ there

Sherlock9

Noted. Thanks

ngn

@Sherlock9 28 bytes: {2=≢∪⍵∨⍳⍵}|+.×0∘∊⊃|{⍺⍵}3=4||

it turned out ⊃ is even better :)

(⎕io←0)

Sherlock9

@ngn Huh. What's going on here?

ngn

14:48

@Sherlock9 ...⊃...{⍺⍵}... is like an if-then-else with swapped then and else: if 0∘∊ then 3=4|| else |

Sherlock9

@ngn Huh. Alright, I'll include this in the post. Thanks

Okay how do I put this into TIO with my test cases? The full program idiom?

ngn

@Sherlock9 it's a train, you can assign it with f← just like any other function

Sherlock9

Ah okay

Not sure this explanation is correct but hopefully it's fine

ngn

15:14

@Sherlock9 looks good to me

2 hours later…

Cows quack

17:31

@ngn what is the reasoning for having a⌹b ←→ (⌹b)+.×a instead of a+.×⌹b?

ngn

⋄⎕rl←1⋄n←3⋄a←?n n⍴0⋄b←?n n⍴0⋄⎕←(a⌹b)((⌹b)+.×a)(a+.×⌹b)

Dyalog APL

@ngn
┌────────────────────────────────────────────┬────────────────────────────────────────────┬────────────────────────────────────────┐
│¯0.5336025183   0.01914628213  0.03256685062│¯0.5336025183   0.01914628213  0.03256685062│0.1462980048  0.9026670489 ¯0.4139653465│
│ 0.07336985253  1.531237046    1.37654444   │ 0.07336985253  1.531237046    1.37654444   │1.822855274   1.597559387  ¯1.028418944 │
│ 2.548101392   ¯0.7141881787  ¯0.02078103805│ 2.548101392   ¯0.7141881787  ¯0.02078103805│0.04845015079 2.713018794  ¯0.7670039015│

ngn

@Cowsquack ^ the output didn't get formatted nicely, but i hope you can see that the first and second matrices are the same, and the third is different

or... did i misunderstand the question? are you asking why ⌹ was designed that way (to return the left inverse rather than the right)? i have no idea

actually, i used wrong terminology above. ⌹b is both "left inverse" and "right inverse" of b. there's a theorem that says those always match.

however, matrix division could be "left" or "right" and for some reason dyalog have chosen "left".

Kritixi Lithos

18:32

@ngn yes, my intended question was on the design choice

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