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

@Sherlock9 4| -> 4||

Thanks!

@Sherlock9 a guard is better than ⍣ there

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

it turned out ⊃ is even better :)

(⎕io←0)

@ngn Huh. What's going on here?

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

@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?

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

Ah okay

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

@Sherlock9 looks good to me

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

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

@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│

@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".

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