Problem with J function in Rosetta Code for Moebius function

[Michael Day]

A recent message in the stream: "[Jforum] Fw: OEIS A240563 - prime
concatenation" mentions

https://rosettacode.org/wiki/M%C3%B6bius_function     (Moebius for
non-German readers!)

I noticed that Rosetta's current J proposal,
   mu=: */@:-@~:@q:
doesn't work,  because of a change in the output of q: on an array - the
right padding is
now 1s rather than 0s;  I forget how to get round the problem.)

mu DOES work ok if you force the rank to be zero:

   mu"0 >: i.20
1 _1 _1 0 _1 1 _1 0 0 1 _1 0 _1 1 1 0 _1 0 _1 0

but the Rosetta example,  without explicit rank,  now results as follows:

   mu >: i. 10 20
1

Over to Raul maybe?

Mike


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[Raul Miller]

Ok, but you have posted the solution right there.

(Add "0 to the definition.)

That said, I really need to spin up my computer (power cord went missing during recovery from plumbing accident).

Thanks,

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Raul

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[Mike Day]

Not in the Rosetta code page!  I haven't got the Chutzpah to 

venture there.

I'd hoped to avoid "0,  but Henry's comment suggests he's 

ok with it!

Good luck with the hydrocybernetics,  aka PbI,  

Mike

Sent from my iPad

On 13 Jun 2025, at 10:56, Raul Miller <rauld...@gmail.com> wrote:



[Henry Rich]

The 9.6 ReleaseNotes https://code.jsoftware.com/wiki/System/ReleaseNotes/J9.6#Changes_to_the_J_engine says

incompatible language change: rank of q: changed to _ 0 0. With the monadic rank 0, as formerly, fill produced invalid results.

That tells you that the fix is to revert to rank 0.

Henry Rich