“probably, earlier versions of J). “ :
FWIW, on this iPad, running J701, so changing {{}} to 3 : 0 .... ),
(and pritchard to pritch!), I get the same results.
Mike
Sent from my iPad
> On 27 Aug 2022, at 02:51, Raul Miller <[email protected]> wrote:
>
> I'm seeing strange behavior with sparse arrays, and I have been mostly
> unsuccessful in simplifying code exhibiting the problem. Thus:
>
> pritch=: {{
> spokes=. $.,1
> primes=. i.0
> while. y > #spokes do.
> primes=. primes, p=. 2+(}.spokes) i.1 NB. find next prime
> rim=. #spokes NB. "length" of "circumference" of wheel
> spokes=. (y<.p*rim)$spokes NB. roll next larger wheel
> spokes=. 0 ((#~ y>])_1+p*1+i.rim)} spokes
> end.
> NB. elided code here
> primes,1+}.,I.spokes
> }}
>
> pritchard 20
> 2 3 5 7 11 13 17 19
>
> pritch8=: {{
> spokes=. $.,1
> primes=. i.0
> while. y > #spokes do.
> primes=. primes, p=. 2+(}.spokes) i.1 NB. find next prime
> rim=. #spokes NB. "length" of "circumference" of wheel
> spokes=. (y<.p*rim)$spokes NB. roll next larger wheel
> spokes=. 8 $. 0 ((#~ y>])_1+p*1+i.rim)} spokes
> end. NB. elided code here
> primes,1+}.,I.spokes
> }}
> pritch8 20
> 2 2 3 5 7 11 13 17 19
>
> Somehow the value for p is different when 8 $. is present in this
> particular implementation (though I don't observe similar behavior in
> similar uses of 8 $. y).
>
> I'm reporting this on the beta forum, but it's an issue in J903 (and,
> probably, earlier versions of J).
>
> FYI,
>
> --
> Raul
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